| 1 | Mastercard Europe Services LIMITED | Unitedkingdom | Moorgate | 7th Floor | London | EC4R 3AB | vocalink.***** | 2014 | $2,268,564,047 | 4 | N/A | N/A | N/A |
| 2 | Icon Clinical (UK) LIMITED | Unitedkingdom | Southcote | 3rd Floor | Reading | RG2 6GP | logianalytics.***** | 1996 | $431,013,156 | 1,588 | N/A | N/A | N/A |
| 3 | Immunocore LIMITED | Unitedkingdom | Abingdon | 92 Park Drive | Oxfordshire | OX14 4RY | immunocore.***** | 2007 | $349,975,308 | 349 | N/A | N/A | N/A |
| 4 | Labcorp Early Development Laboratories LIMITED | Unitedkingdom | Fewston | Otley Road | North Yorkshire | HG3 1PY | labcorp.***** | 1974 | $327,798,694 | 3,016 | N/A | N/A | N/A |
| 5 | Fugro Gb (north) Marine LIMITED | Unitedkingdom | Denmore | Survey House | Aberdeen City | AB23 8JW | fugro.***** | 1979 | $264,888,492 | 727 | N/A | N/A | N/A |
| 6 | Sgs United Kingdom LIMITED | Unitedkingdom | Ellesmere Port | Inward Way | Cheshire West and Chester | CH65 3EN | sgs.***** | 1974 | $196,981,303 | 1,386 | N/A | N/A | N/A |
| 7 | Its Testing Services (UK) LIMITED | Unitedkingdom | Kelvedon Hatch | Academy Place | Essex | CM14 5NQ | intertech.***** | 1979 | $190,303,154 | 1,770 | N/A | N/A | N/A |
| 8 | Hyland UK Operations LIMITED | Unitedkingdom | Maidenhead | The Place | Windsor and Maidenhead | SL6 1AF | alfresco.***** | 2002 | $140,478,000 | 490 | N/A | N/A | N/A |
| 9 | Intertek Testing Services Pacific LIMITED | Unitedkingdom | Marylebone | 25 Savile Row | London | W1S 2ES | N/A | 2008 | $126,908,558 | 3 | N/A | N/A | N/A |
| 10 | Turner & Townsend Partners Llp | Unitedkingdom | Collingham | Low Hall | Leeds, West Yorkshire | LS18 4GH | turnerandtownsend.***** | 2015 | $103,140,944 | 134 | N/A | N/A | N/A |
| 11 | Royal Society Of Chemistry (the) | Unitedkingdom | Marylebone | Royal Society of Chemistry | London | W1J 0BA | rsc.***** | 1841 | $88,319,891 | 735 | N/A | N/A | N/A |
| 12 | British Engineering Services LIMITED | Unitedkingdom | Warrington | Unit 718 | Warrington | WA3 6BA | N/A | 2014 | $76,304,258 | 751 | N/A | N/A | N/A |
| 13 | Eurofins Forensic Services LIMITED | Unitedkingdom | Wolverhampton | I54 Valiant Way Business Park | Wolverhampton, West Midlands | WV9 5GB | eurofins.***** | 2017 | $72,545,638 | 707 | N/A | N/A | N/A |
| 14 | Hpi LIMITED | Unitedkingdom | Leeds | 8a Platform | Leeds, West Yorkshire | LS1 4JB | N/A | 1938 | $68,651,290 | 372 | N/A | N/A | N/A |
| 15 | Cell Therapy Catapult LIMITED | Unitedkingdom | Rotherhithe | Guys Hospital | London | SE1 9RT | ct.***** | 2012 | $67,929,166 | 406 | N/A | N/A | N/A |
| 16 | Warringtonfire Testing And Certification LIMITED | Unitedkingdom | Marylebone | 3rd Floor | London | WC2E 7HA | N/A | 2018 | $67,870,870 | 400 | N/A | N/A | N/A |
| 17 | Restore Digital LIMITED | Unitedkingdom | Bilston | Village Way | Wolverhampton, West Midlands | WV14 0UJ | edmgroup.***** | 2003 | $56,251,612 | 694 | N/A | N/A | N/A |
| 18 | Applus UK LTD | Unitedkingdom | Grangemouth | Westmains Industrial Estate | Falkirk | FK3 8YE | applustraining.***** | 2002 | $50,656,420 | 419 | N/A | N/A | N/A |
| 19 | Utec Ncs Survey LIMITED | Unitedkingdom | Aberdeen | 2 Marischal Square | Aberdeen City | AB10 1DQ | N/A | 2006 | $49,494,687 | 245 | N/A | N/A | N/A |
| 20 | Fulkrum Technical Resources LTD | Unitedkingdom | Ladbroke Grove | Office 4 | London | W8 6BD | fulkrum.***** | 2011 | $47,090,779 | 64 | N/A | N/A | N/A |
| 21 | Docusign UK LIMITED | Unitedkingdom | Moorgate | 1st Floor | London | EC2A 2DX | docusign.***** | 2016 | $43,643,273 | 99 | N/A | N/A | N/A |
| 22 | Crisil Irevna UK LIMITED | Unitedkingdom | Moorgate | Farringdon | London | EC1A 9DD | crisil.***** | 2000 | $43,559,567 | 127 | N/A | N/A | N/A |
| 23 | Dnaco LIMITED | Unitedkingdom | Wolverhampton | Unit G1 Business Park | Wolverhampton, West Midlands | WV9 5GB | N/A | 2018 | $43,451,068 | 558 | N/A | N/A | N/A |
| 24 | Ul Vs LIMITED | Unitedkingdom | Lychpit | Unit 1-3 Horizon Kingsland Business Park | Hampshire | RG24 8AH | ul.***** | 1987 | $40,179,716 | 342 | N/A | N/A | N/A |
| 25 | Phs Compliance LIMITED | Unitedkingdom | Golborne | Golborne Enterprise Park Kid Glove Road | Manchester, Greater Manchester | WA3 3GR | phscompliance.***** | 1999 | $39,249,378 | 482 | N/A | N/A | N/A |
| 26 | Chippenham Motor Company LIMITED | Unitedkingdom | Hullavington | Bumpers Way | Wiltshire | SN14 6LF | chippenhammotor.***** | 1985 | $38,414,215 | 270 | N/A | N/A | N/A |
| 27 | Tersus Consultancy LIMITED | Unitedkingdom | Rainham | 1st Floor, Rainham House | London | RM13 8RH | tersusgroup.***** | 1985 | $37,544,201 | 338 | N/A | N/A | N/A |
| 28 | Pass (portable Appliance Safety Services) LTD | Unitedkingdom | Aislaby | 1 Wilson Street | Stockton-on-tees | TS17 7AR | pass.***** | 2002 | $36,079,558 | 112 | N/A | N/A | N/A |
| 29 | Redspeed USA LIMITED | Unitedkingdom | Stepney | Quadrant House Floor 6 | London | E1W 1YW | N/A | 2016 | $35,716,893 | 136 | N/A | N/A | N/A |
| 30 | Iqvia Ies UK LIMITED | Unitedkingdom | Reading | 3 Forbury Place | Reading | RG1 3JH | iqvia.***** | 1987 | $35,202,261 | 336 | N/A | N/A | N/A |
| 31 | Stan Robinson Group LIMITED | Unitedkingdom | Bradley | Airfield Industrial Estate Newport Road | Staffordshire | ST18 9NR | stanrobinson.***** | 1970 | $32,672,463 | 294 | N/A | N/A | N/A |
| 32 | Bre Certification | Unitedkingdom | Chiswell Green | Building 17 | Hertfordshire | WD25 9NH | bregroup.***** | 1998 | $32,093,378 | 600 | N/A | N/A | N/A |
| 33 | Exponent International LIMITED | Unitedkingdom | Burton Leonard | Hornbeam Bus. | North Yorkshire | HG2 8RE | exponent.***** | 2001 | $31,934,881 | 150 | N/A | N/A | N/A |
| 34 | Oeg Renewables LIMITED | Unitedkingdom | Caister-on-sea | Yarmouth Business Park | Norfolk | NR31 0DN | N/A | 2006 | $30,081,204 | 106 | N/A | N/A | N/A |
| 35 | Parklands LIMITED | Unitedkingdom | Grantown-on-spey | Rosehall the Square | Highland | PH26 3HG | parklandsgroup.***** | 1993 | $28,870,854 | 701 | N/A | N/A | N/A |
| 36 | Als Inspection UK LIMITED | Unitedkingdom | Prescot | Knowsley Industrial Estate | Knowsley, Merseyside | L34 9HP | alsglobal.***** | 1975 | $28,514,386 | 158 | N/A | N/A | N/A |
| 37 | Hydrosave UK LIMITED | Unitedkingdom | Kettering | 4 Swallow Court | Northamptonshire | NN15 6XX | hydrosave.***** | 1903 | $28,070,197 | 400 | N/A | N/A | N/A |
| 38 | Intertek Testing Services Holdings LIMITED. | Unitedkingdom | Kelvedon Hatch | 1-9 Brook Street | Essex | CM14 5NQ | intertech.***** | 1996 | $27,858,861 | 26 | N/A | N/A | N/A |
| 39 | Abzena (cambridge) LIMITED | Unitedkingdom | Chesterton | Babraham Research Campus | Cambridgeshire | CB22 3AT | abzena.***** | 2004 | $27,804,226 | 143 | N/A | N/A | N/A |
| 40 | AS International CORPORATION LTD | Unitedkingdom | Formby | 2b Olympic Way | Sefton, Merseyside | L30 1RD | alexstewartinternational.***** | 1976 | $25,883,222 | 129 | N/A | N/A | N/A |
| 41 | Calibration Services | Unitedkingdom | Smethwick | Soho Foundry | Sandwell, West Midlands | B66 2LP | averyweigh-tronix.***** | 2019 | $25,149,259 | 500 | N/A | N/A | N/A |
| 42 | Cosmetic Warriors LIMITED | Unitedkingdom | Poole | 29 High Street | Poole | BH15 1AB | uk.***** | 2001 | $23,316,399 | 125 | N/A | N/A | N/A |
| 43 | Eurofins Water Hygiene Testing UK LIMITED | Unitedkingdom | Coven | I54 Business Park Valiant Way | Staffordshire | WV9 5GB | farmanalysis.***** | 2015 | $22,773,907 | 175 | N/A | N/A | N/A |
| 44 | Katech Ingredient Solutions LTD | Unitedkingdom | Mickle Trafford | Venture Point | Cheshire West and Chester | CH2 4NE | katech.***** | 2010 | $20,639,460 | 25 | N/A | N/A | N/A |
| 45 | Key Forensic Services LIMITED | Unitedkingdom | Altrincham | Corpacq House | Manchester, Greater Manchester | WA14 1DW | keyforensic.***** | 2018 | $18,936,443 | 217 | N/A | N/A | N/A |
| 46 | Aptuit | Unitedkingdom | Riccarton | Research Avenue South | City of Edinburgh | EH14 4AP | aptuit.***** | 2011 | $18,920,983 | 350 | N/A | N/A | N/A |
| 47 | B S Marson And Sons LIMITED | Unitedkingdom | Newcastle-under-lyme | Deansgate Garage | Staffordshire | ST5 2HN | bsmarson.***** | 1957 | $18,918,582 | 45 | N/A | N/A | N/A |
| 48 | Catalent Nottingham LIMITED | Unitedkingdom | Thorneywood | 8 Orchard Place | Nottingham | NG8 6PX | catalent.***** | 1997 | $18,462,412 | 185 | N/A | N/A | N/A |
| 49 | Tag International Development LIMITED | Unitedkingdom | London | 63-65 Petty France | London | SW1H 9EU | vodohod.***** | 2010 | $17,938,746 | 74 | N/A | N/A | N/A |
| 50 | Socotec Asbestos LIMITED | Unitedkingdom | Hanbury Woodend | Socotec House, Bretby Business Park | Staffordshire | DE15 0YZ | socotec.***** | 2003 | $17,610,880 | 188 | N/A | N/A | N/A |
| 51 | Napit Registration LIMITED | Unitedkingdom | Mansfield | 4th Floor | Nottinghamshire | NG19 8RL | napit.***** | 1994 | $16,715,815 | 6 | N/A | N/A | N/A |
| 52 | Intertek Testing Management LTD | Unitedkingdom | Marylebone | 33 Cavendish Square | London | W1G 0PS | gpe.***** | 1969 | $15,855,421 | 64 | N/A | N/A | N/A |
| 53 | Environmental Essentials LIMITED | Unitedkingdom | Newcastle-under-lyme | Unit 3 Arlington Court | Staffordshire | ST5 6SS | learnbyee.***** | 2004 | $15,007,076 | 132 | N/A | N/A | N/A |
| 54 | R3 LIMITED | Unitedkingdom | Moorgate | 2 London Wall Place | London | EC2Y 5AU | r3.***** | 2016 | $14,592,750 | 214 | N/A | N/A | N/A |
| 55 | Wallstreetdocs LTD | Unitedkingdom | Canary Wharf | Level 3 | London | E14 5NR | wsd.***** | 2008 | $14,442,890 | 142 | N/A | N/A | N/A |
| 56 | Guardian Water Treatment LTD | Unitedkingdom | Basildon | 8-10 Capricorn Centre Cranes Farm Road | Essex | SS14 3JJ | gwtltd.***** | 2001 | $14,214,476 | 110 | N/A | N/A | N/A |
| 57 | Dekra UK LTD | Unitedkingdom | Chilworth | Phi House | Hampshire | SO16 7NS | dekra-uk.***** | 1986 | $14,066,368 | 137 | N/A | N/A | N/A |
| 58 | Domainex LIMITED | Unitedkingdom | Saffron Walden | Churchill Building | Essex | CB10 1XL | domainex.***** | 2001 | $13,991,646 | 117 | N/A | N/A | N/A |
| 59 | Megger Aftersales Service | Unitedkingdom | Eastry | Channel View Road | Kent | CT17 9TP | megger.***** | 2019 | $13,514,989 | 250 | N/A | N/A | N/A |
| 60 | York Bioanalytical Solutions LIMITED | Unitedkingdom | Nether Poppleton | Cedar House | York | YO26 6QR | yorkbio.***** | 1999 | $13,486,849 | 81 | N/A | N/A | N/A |
| 61 | Forensic Science Regulator | Unitedkingdom | Aston | 23 Stephenson Street | Birmingham, West Midlands | B2 4BJ | N/A | 1993 | $13,372,241 | 250 | N/A | N/A | N/A |
| 62 | Aughton Automation LIMITED | Unitedkingdom | Central | Venture Point Bus. | Liverpool, Merseyside | L24 9PB | aughton.***** | 1999 | $13,147,880 | 77 | N/A | N/A | N/A |
| 63 | Nielsen Sports UK And Ireland LIMITED | Unitedkingdom | Saint Giles | 5th Floor Endeavour House | London | WC2H 8JR | nielsen.***** | 1983 | $12,868,195 | 52 | N/A | N/A | N/A |
| 64 | Eurofins Chemtest LIMITED | Unitedkingdom | Newmarket | Depot Road | Suffolk | CB8 0AL | chemtest.***** | 1962 | $12,702,174 | 142 | N/A | N/A | N/A |
| 65 | Kirkman Utility Services LTD | Unitedkingdom | Gorgie | 24 Rutland Street | City of Edinburgh | EH1 2AN | N/A | 2007 | $12,512,961 | 47 | N/A | N/A | N/A |
| 66 | Charnwood Molecular LIMITED | Unitedkingdom | Leeds | 8th Floor Central Square | Leeds, West Yorkshire | LS1 4DL | charnwood-molecular.***** | 1998 | $11,576,419 | 116 | N/A | N/A | N/A |
| 67 | Butterworth Laboratories LIMITED | Unitedkingdom | Teddington | 54-56 Waldegrave Road | London | TW11 8NY | butterworth-labs.***** | 1974 | $11,157,793 | 86 | N/A | N/A | N/A |
| 68 | Csa Group Testing UK LIMITED | Unitedkingdom | Garden City | Unit 6, Hawarden Industrial Park | Flintshire | CH5 3US | csagroupuk.***** | 1997 | $11,140,518 | 88 | N/A | N/A | N/A |
| 69 | Synergy Construction And Property Consultants Llp | Unitedkingdom | Guildford | 8-9 Faraday Road | Surrey | GU1 1EA | synergyllp.***** | 2006 | $11,069,842 | 98 | N/A | N/A | N/A |
| 70 | Osentia LIMITED | Unitedkingdom | Clapton | 3rd Floor | London | EC2A 4NE | N/A | 2023 | $10,987,712 | 2 | N/A | N/A | N/A |
| 71 | Cansford Laboratories LIMITED | Unitedkingdom | Llanedeyrn | Unit 1a Pentwyn Business Centre | Cardiff | CF23 7HB | cansfordlabs.***** | 2010 | $10,563,314 | 91 | N/A | N/A | N/A |
| 72 | Intertek Medical Notified Body AB | Unitedkingdom | Kelvedon Hatch | Academy Place 1-9 Brook Street | Essex | CM14 5NQ | N/A | 2018 | $9,635,673 | 28 | N/A | N/A | N/A |
| 73 | Wuxi Apptec UK LTD | Unitedkingdom | Moorgate | 5 New Street Square | London | EC4A 3TW | N/A | 2011 | $9,405,597 | 37 | N/A | N/A | N/A |
| 74 | Almac Sciences (scotland) LIMITED | Unitedkingdom | Penicuik | 5 the Fleming Building | Midlothian | EH26 0BE | almacgroup.***** | 1994 | $9,404,471 | 51 | N/A | N/A | N/A |
| 75 | Photolox LIMITED | Unitedkingdom | Edinburgh | Level 5 | City of Edinburgh | EH3 8RY | loxleycolour.***** | 2011 | $9,209,613 | 78 | N/A | N/A | N/A |
| 76 | Bsria Cert LIMITED | Unitedkingdom | Bracknell | Old Bracknell Lane West | Bracknell Forest | RG12 7AH | bsria.***** | 2009 | $9,093,124 | 170 | N/A | N/A | N/A |
| 77 | 3c Test LIMITED | Unitedkingdom | Burton Latimer | Silverstone Technology Park | Northamptonshire | NN12 8GX | 3ctest.***** | 1987 | $8,992,979 | 66 | N/A | N/A | N/A |
| 78 | Geoff Smith Associates LIMITED | Unitedkingdom | Coalville | Unit 5, Cartwright Court | Leicestershire | LE67 1UE | gsaltd.***** | 1997 | $8,740,754 | 77 | N/A | N/A | N/A |
| 79 | Ausden Clark LIMITED | Unitedkingdom | Braunstone Town | Transport House | Leicester | LE3 1UW | ausdenclark.***** | 1972 | $8,676,383 | 66 | N/A | N/A | N/A |
| 80 | Storetec Services LIMITED | Unitedkingdom | Bransholme | Sidings Business Park | City of Kingston-upon-hull | HU3 4XA | storetec.***** | 2003 | $8,628,621 | 69 | N/A | N/A | N/A |
| 81 | Qinetiq Target Services LIMITED | Unitedkingdom | Farnborough | Cody Technology Park Old Ively Road | Hampshire | GU14 0LX | qinetiq.***** | 2006 | $8,474,135 | 79 | N/A | N/A | N/A |
| 82 | R & A Kay Inspection Services LIMITED | Unitedkingdom | Stockton-on-tees | Trident House,falcon Court | Stockton-on-tees | TS18 3TX | rakinspection.***** | 1984 | $8,286,122 | 33 | N/A | N/A | N/A |
| 83 | Marchwood Scientific Services LIMITED | Unitedkingdom | Upper Shirley | 371 Millbrook Road West | Southampton | SO15 0HW | marchwood-scientific.***** | 1998 | $8,112,852 | 57 | N/A | N/A | N/A |
| 84 | Broughton Life Sciences LIMITED | Unitedkingdom | Earby | Oak Tree House | Lancashire | BB18 6JZ | broughton-group.***** | 2006 | $8,036,856 | 78 | N/A | N/A | N/A |
| 85 | C T O Engineering Workshops | Unitedkingdom | Wheal Rose | Western Group Centre | Cornwall | TR16 5EH | N/A | 2020 | $7,974,548 | 150 | N/A | N/A | N/A |
| 86 | Eurofins Genomics Europe Dtc - Population Genetics Products & Services LIMITED | Unitedkingdom | Wolverhampton | I54 Valiant Way Business Park | Wolverhampton, West Midlands | WV9 5GB | eurofins.***** | 2022 | $7,947,098 | 23 | N/A | N/A | N/A |
| 87 | British Engineering Services Asset Reliability LIMITED | Unitedkingdom | Manvers | Unit 3a,adwick Park | Rotherham, South Yorkshire | S63 5AB | pcmseng.***** | 2003 | $7,850,048 | 93 | N/A | N/A | N/A |
| 88 | Element Materials Technology Sheffield LTD | Unitedkingdom | Rotherham | 3 Ignite Magna Way | Rotherham, South Yorkshire | S601FD | element.***** | 1880 | $7,632,861 | 77 | N/A | N/A | N/A |
| 89 | Eurofins Professional Scientific Services UK LIMITED | Unitedkingdom | Coven | Unit G1 Valiant Way | Staffordshire | WV9 5GB | eurofins.***** | 2017 | $7,522,425 | 97 | N/A | N/A | N/A |
| 90 | Alpha Biolaboratories Legal LIMITED | Unitedkingdom | Old Hall | Unit 14 Webster Court | Warrington | WA5 8WD | alphabiolabs.***** | 2012 | $7,490,764 | 51 | N/A | N/A | N/A |
| 91 | Envirolab LIMITED | Unitedkingdom | Frodsham | R S K Group Ltd | Cheshire West and Chester | WA6 0AR | envirolabs.***** | 2002 | $7,329,780 | 76 | N/A | N/A | N/A |
| 92 | Basec Group LIMITED | Unitedkingdom | Crownhill | Presley House | Milton Keynes | MK8 0ES | basec.***** | 1971 | $6,906,859 | 73 | N/A | N/A | N/A |
| 93 | Hydro International Data, Insight & Analysis LTD | Unitedkingdom | Clevedon | Hydro International Ltd | North Somerset | BS21 6FT | hydro-int.***** | 1995 | $6,901,909 | 78 | N/A | N/A | N/A |
| 94 | Printspace Studios LIMITED | Unitedkingdom | Shoreditch | 74 Kingsland Road | London | E2 8DL | theprintspace.***** | 2007 | $6,865,313 | 28 | N/A | N/A | N/A |
| 95 | Quicklight LIMITED | Unitedkingdom | Thatcham | Crown House | West Berkshire | RG19 4PL | quicklight.***** | 1994 | $6,771,562 | 96 | N/A | N/A | N/A |
| 96 | Memorial-Diamonds.com | Unitedkingdom | Tytherington | Sunrise House | Cheshire East | SK10 2LP | phoenix-memorial-diamonds.***** | 2012 | $6,645,456 | 125 | N/A | N/A | N/A |
| 97 | Eurofins Product Testing Services LIMITED | Unitedkingdom | Coven | I54 Business Park | Staffordshire | WV9 5GB | eurofins.***** | 2010 | $6,566,593 | 91 | N/A | N/A | N/A |
| 98 | Wescott Industrial Services LTD | Unitedkingdom | Jarrow | Unit 9b | South Tyneside, Tyne and Wear | NE32 3UP | wescottcoatings.***** | 2010 | $6,428,332 | 32 | N/A | N/A | N/A |
| 99 | Vehicle Quality Solutions LIMITED | Unitedkingdom | Chellaston | Unit 6, Redwing Court | Derby | DE74 2UH | N/A | 2001 | $6,372,865 | 95 | N/A | N/A | N/A |
| 100 | Document Logistix LIMITED | Unitedkingdom | Tilbrook | Tokairo House, 8 Copperhouse Court, Caldecotte | Milton Keynes | MK7 8NL | document-logistix.***** | 2010 | $6,331,000 | 42 | N/A | N/A | N/A |