| 1 | Longstaff And Shaw (heating) LIMITED | Unitedkingdom | Croydon | 602 Purley Way | London | CR0 4RF | N/A | 1968 | $2,676,912,418 | 69 | N/A | N/A | N/A |
| 2 | Scotia Gas Networks LIMITED | Unitedkingdom | Horley | St Lawrence House | Surrey | RH6 9HJ | sgn.***** | 2003 | $1,603,494,986 | 4,865 | N/A | N/A | N/A |
| 3 | Northern Gas Networks LIMITED | Unitedkingdom | Pendas Fields | 1100 Century Way | Leeds, West Yorkshire | LS15 8TU | northerngasnetworks.***** | 2004 | $662,358,796 | 1,589 | N/A | N/A | N/A |
| 4 | Ovo (s) Gas LIMITED | Unitedkingdom | Bristol | Temple Quay | City of Bristol | BS1 6DG | N/A | 1992 | $615,240,316 | 353 | N/A | N/A | N/A |
| 5 | The Bss Group LIMITED | Unitedkingdom | King'S Heath | Lodge Way House | Northamptonshire | NN5 7UG | bssindustrial.***** | 1899 | $582,499,879 | 1,206 | N/A | N/A | N/A |
| 6 | Cbre Gws LIMITED | Unitedkingdom | Rotherhithe | 61 Southwark Street | London | SE1 0HL | cbre.***** | 1960 | $556,492,115 | 1,950 | N/A | N/A | N/A |
| 7 | Scotland Gas Networks PLC | Unitedkingdom | Newbridge | Axis House | North Yorkshire | EH28 8TG | sgn.***** | 2004 | $488,284,210 | 151 | N/A | N/A | N/A |
| 8 | British Gas New Heating LIMITED | Unitedkingdom | Stockport | Newbridge Lane | Manchester, Greater Manchester | SK1 2GT | britishgas.***** | 2008 | $437,043,511 | 1,771 | N/A | N/A | N/A |
| 9 | Ui Central Holdings LIMITED | Unitedkingdom | Wright'S Green | Building 4 Clearwater | Warrington | WA5 3UZ | unitedliving.***** | 2004 | $387,269,222 | 783 | N/A | N/A | N/A |
| 10 | Homeserve Membership LIMITED | Unitedkingdom | Shelfield | Cable Drive | Walsall, West Midlands | WS2 7BN | homeserve.***** | 1992 | $365,442,296 | 1,885 | N/A | N/A | N/A |
| 11 | Bouygues E&S Contracting UK LIMITED | Unitedkingdom | Motherwell | Excel House | North Lanarkshire | ML1 4UF | bouygues-es.***** | 1984 | $264,292,831 | 492 | N/A | N/A | N/A |
| 12 | Vaillant Industrial UK LIMITED | Unitedkingdom | Belper | Vaillant Group | Derbyshire | DE56 1JT | vaillant.***** | 1972 | $258,475,289 | 214 | N/A | N/A | N/A |
| 13 | Conex Universal LIMITED | Unitedkingdom | Kingswinford | Building 95 | Dudley, West Midlands | DY6 7FT | conexbanninger.***** | 2011 | $228,004,122 | 81 | N/A | N/A | N/A |
| 14 | B.H.C. LIMITED | Unitedkingdom | Lanark | Medwyn Park | South Lanarkshire | ML11 8HS | bhc.***** | 1995 | $176,664,202 | 432 | N/A | N/A | N/A |
| 15 | Liberty Group Investments LIMITED | Unitedkingdom | Cronton | Garden Works | Knowsley, Merseyside | L33 7SG | libertygasgroup.***** | 1969 | $139,984,212 | 1,226 | N/A | N/A | N/A |
| 16 | Stelrad LIMITED | Unitedkingdom | Swinton | Stelrad House, Marriott Road | Rotherham, South Yorkshire | S64 8BN | stelrad.***** | 1936 | $137,243,056 | 194 | N/A | N/A | N/A |
| 17 | Carrier Solutions UK LTD. | Unitedkingdom | Barne Barton | Belliver Industrial Estate | Plymouth | PL6 7DB | toshiba-aircon.***** | 1999 | $136,466,056 | 505 | N/A | N/A | N/A |
| 18 | Borley Engineering Services LIMITED | Unitedkingdom | Tremorfa | Alexandra Gate | Cardiff | CF24 2SA | cmbengineering.***** | 1992 | $135,530,995 | 336 | N/A | N/A | N/A |
| 19 | Sureserve Compliance Central LIMITED | Unitedkingdom | Paddington | 13 Norfolk Place | London | W2 1QJ | N/A | 1994 | $109,837,370 | 622 | N/A | N/A | N/A |
| 20 | Purmo Group (UK) LTD | Unitedkingdom | Lamesley | Eastern Avenue | Gateshead, Tyne and Wear | NE11 0PG | myson.***** | 1960 | $101,851,190 | 344 | N/A | N/A | N/A |
| 21 | Quooker UK LTD | Unitedkingdom | Millennium Quarter | Beaumont Building | Manchester, Greater Manchester | M3 1PQ | quooker.***** | 2004 | $100,537,484 | 117 | N/A | N/A | N/A |
| 22 | British Gas Social Housing LIMITED | Unitedkingdom | Windsor | Millstream | Windsor and Maidenhead | SL4 5GD | britishgas.***** | 1963 | $98,476,073 | 472 | N/A | N/A | N/A |
| 23 | Sutton And East Surrey Water Services LIMITED | Unitedkingdom | Redhill | 66-74 London Road | Surrey | RH1 1LJ | h2oservices.***** | 1989 | $87,223,240 | 376 | N/A | N/A | N/A |
| 24 | Sungrow Power UK LIMITED | Unitedkingdom | Milton Keynes | Unit 2 Moorgate House | Milton Keynes | MK9 1JL | N/A | 2014 | $86,406,109 | 39 | N/A | N/A | N/A |
| 25 | Sureserve Compliance South LIMITED | Unitedkingdom | Paddington | 13 Norfolk Place | London | W2 1QJ | N/A | 2004 | $85,365,090 | 482 | N/A | N/A | N/A |
| 26 | Ics Cool Energy LIMITED | Unitedkingdom | Testwood | Calmore Industrial Estate | Hampshire | SO40 3SA | icscoolenergy.***** | 2005 | $79,876,643 | 337 | N/A | N/A | N/A |
| 27 | Liberty Gas Group LIMITED | Unitedkingdom | Cronton | Charleywood Road | Knowsley, Merseyside | L33 7SG | liberty-group.***** | 2001 | $79,167,144 | 689 | N/A | N/A | N/A |
| 28 | Bgis Global Integrated Solutions LIMITED | Unitedkingdom | London | Suite 1 7th Floor | London | SW1H 0BL | N/A | 1989 | $75,572,213 | 352 | N/A | N/A | N/A |
| 29 | Cubicworks LTD | Unitedkingdom | Salford | 2nd Floor Spinnaker Court | Manchester, Greater Manchester | M50 2YR | N/A | 2019 | $74,424,736 | 234 | N/A | N/A | N/A |
| 30 | T Brown Group LIMITED | Unitedkingdom | Leatherhead | Leith House | Surrey | KT22 7AB | tbrown.***** | 1971 | $70,402,999 | 382 | N/A | N/A | N/A |
| 31 | Sureserve Compliance Northwest LIMITED | Unitedkingdom | Garston | Unit 16 | Liverpool, Merseyside | L19 2RF | suregroup.***** | 2000 | $64,878,911 | 477 | N/A | N/A | N/A |
| 32 | The James Mercer Group LIMITED | Unitedkingdom | Larches | Tulketh Hall Works | Lancashire | PR2 2RB | jamesmercergroup.***** | 2000 | $59,752,221 | 241 | N/A | N/A | N/A |
| 33 | G & A Barnie Group LIMITED | Unitedkingdom | Inverness | 16 Carsegate Road South Carsegate Industrial Estate | Highland | IV3 8LL | gabarnie.***** | 2004 | $59,273,258 | 386 | N/A | N/A | N/A |
| 34 | Swale Heating LIMITED | Unitedkingdom | Sittingbourne | Eurolink Industrial Estate Heard Way | Kent | ME10 3SA | swaleheating.***** | 1972 | $57,171,859 | 356 | N/A | N/A | N/A |
| 35 | Volution Ventilation Group LIMITED | Unitedkingdom | Crawley | Fleming Way | West Sussex | RH10 9YX | vent-axia.***** | 1933 | $56,286,314 | 29 | N/A | N/A | N/A |
| 36 | Phs Home Solutions LIMITED | Unitedkingdom | Houghton-le-spring | The Venter Building | Sunderland, Tyne and Wear | DH4 5RA | pacificagroup.***** | 2010 | $54,397,538 | 213 | N/A | N/A | N/A |
| 37 | Robert Heath Heating LIMITED | Unitedkingdom | Aberystwyth | Unit 10c | Ceredigion | SY23 3AH | robertheath.***** | 1983 | $54,032,077 | 284 | N/A | N/A | N/A |
| 38 | Mechanical Services LIMITED | Unitedkingdom | Croydon | Merlin House | London | CR0 4RF | hamechanicalservices.***** | 1985 | $53,189,491 | 142 | N/A | N/A | N/A |
| 39 | Pimlico Plumbers LIMITED | Unitedkingdom | Herne Hill | Pimlico House | London | SE11 6NQ | pimlicoplumbers.***** | 1979 | $53,109,987 | 142 | N/A | N/A | N/A |
| 40 | Forefront Utilities LIMITED | Unitedkingdom | Navestock | Jenkins Farm | Essex | RM4 1HL | forefrontutilities.***** | 1989 | $52,725,938 | 94 | N/A | N/A | N/A |
| 41 | Morrow Contracts LIMITED | Unitedkingdom | Gortgrib | 37 Rocky Road | Belfast | BT5 7TA | morrowgroup.***** | 1975 | $51,501,300 | 172 | N/A | N/A | N/A |
| 42 | Vaughan Engineering LIMITED | Unitedkingdom | Hebburn | 14 Blue Sky Way Monkton Business Park South | South Tyneside, Tyne and Wear | NE31 2EQ | vaughan-group.***** | 1972 | $47,601,863 | 214 | N/A | N/A | N/A |
| 43 | Colt International LIMITED | Unitedkingdom | Weston | Colt House Ridgeway Office Park | Hampshire | GU32 3QF | coltinfo.***** | 1931 | $47,582,886 | 279 | N/A | N/A | N/A |
| 44 | James Frew LIMITED | Unitedkingdom | Stevenston | 83 New Street | North Ayrshire | KA20 3HD | gassure.***** | 1961 | $45,803,876 | 399 | N/A | N/A | N/A |
| 45 | Woodford Heating & Energy LIMITED | Unitedkingdom | Loughton | Oakwood House | Essex | IG10 3TZ | woodfordheating.***** | 1994 | $44,634,772 | 114 | N/A | N/A | N/A |
| 46 | Taylor & Fraser LIMITED | Unitedkingdom | Howwood | 117 Abercorn Street | Renfrewshire | PA3 4DH | taylorandfraser.***** | 1906 | $44,092,219 | 255 | N/A | N/A | N/A |
| 47 | Intoheat (holdings) LIMITED | Unitedkingdom | Rudgeway | Units 6/7 Short Way | South Gloucestershire | BS35 3UT | intoheat.***** | 2012 | $42,324,036 | 112 | N/A | N/A | N/A |
| 48 | Mala Engineering LIMITED | Unitedkingdom | Clapton | 9 Hewett Street | London | EC2A 3NN | mala.***** | 1971 | $42,145,561 | 100 | N/A | N/A | N/A |
| 49 | Atlantic Plastics LIMITED | Unitedkingdom | Bridgend | Coytrahene Close | Bridgend | CF31 2AX | talis-uk.***** | 1970 | $40,838,751 | 190 | N/A | N/A | N/A |
| 50 | E Plan Energy LIMITED | Unitedkingdom | Shifnal | Unit C1 | Shropshire | TF11 8PJ | eplanenergy.***** | 2013 | $40,712,541 | 124 | N/A | N/A | N/A |
| 51 | Jcw Energy Services LIMITED | Unitedkingdom | Steeple Morden | Unit 7 | Cambridgeshire | SG8 6DN | jcwes.***** | 2014 | $40,139,580 | 249 | N/A | N/A | N/A |
| 52 | Emtec Southern LIMITED | Unitedkingdom | Redhill | 36 Ormside Way | Surrey | RH1 2LW | t4m-e.***** | 2007 | $39,973,610 | 36 | N/A | N/A | N/A |
| 53 | Hawco LIMITED | Unitedkingdom | Godalming | Lower South Street | Surrey | GU7 1BZ | hawco.***** | 1963 | $38,770,861 | 172 | N/A | N/A | N/A |
| 54 | Fujitsu General Air Conditioning (UK) LIMITED | Unitedkingdom | Borehamwood | Unit 150 | Hertfordshire | WD6 3SG | fujitsu.***** | 1977 | $38,589,858 | 35 | N/A | N/A | N/A |
| 55 | Saltire Facilities Management LIMITED | Unitedkingdom | Bellshill | Carnbroe House | North Lanarkshire | ML4 3PE | saltire.***** | 1986 | $38,476,345 | 285 | N/A | N/A | N/A |
| 56 | Sureserve Compliance North LIMITED | Unitedkingdom | Drumchapel | Queenslie Court | Glasgow City | G33 4DB | gascall.***** | 1996 | $36,507,247 | 261 | N/A | N/A | N/A |
| 57 | S.A.V. United Kingdom LIMITED | Unitedkingdom | Sheerwater | Scandia House | Surrey | GU21 5BX | microsaic.***** | 1953 | $36,073,440 | 102 | N/A | N/A | N/A |
| 58 | Correct Contract Services LIMITED | Unitedkingdom | Eastleigh | Fleming Court | Hampshire | SO50 9PD | correctcs.***** | 2007 | $35,331,219 | 161 | N/A | N/A | N/A |
| 59 | Bsw Heating LTD | Unitedkingdom | Kenley | 3 Old Barn Lane | London | CR8 5AT | bsw-heating.***** | 1972 | $34,933,683 | 215 | N/A | N/A | N/A |
| 60 | Shawston International LIMITED | Unitedkingdom | Booker | Units 8 & 9 Hillbottom Road | Buckinghamshire | HP12 4HS | shawston.***** | 2001 | $34,502,047 | 187 | N/A | N/A | N/A |
| 61 | Gas Fast LIMITED | Unitedkingdom | Watford | Vision House | Hertfordshire | WD24 4JL | N/A | 2002 | $34,157,463 | 48 | N/A | N/A | N/A |
| 62 | Edison House Trading LIMITED | Unitedkingdom | Ipswich | Unit 7 | Suffolk | IP3 9GU | elementshop.***** | 2015 | $33,105,908 | 21 | N/A | N/A | N/A |
| 63 | Paine Manwaring LIMITED | Unitedkingdom | High Salvington | Unit D | West Sussex | BN14 8HQ | painemanwaring.***** | 1992 | $32,550,836 | 106 | N/A | N/A | N/A |
| 64 | Cambridge Maintenance Services LIMITED | Unitedkingdom | Saint Ives | Si One | Cambridgeshire | PE27 4AA | cambridgemaintenance.***** | 1988 | $32,500,467 | 183 | N/A | N/A | N/A |
| 65 | Eni Hewett LIMITED | Unitedkingdom | London | Eni House | London | SW1W 8PZ | N/A | 1984 | $32,216,153 | 100 | N/A | N/A | N/A |
| 66 | Ability Projects LIMITED | Unitedkingdom | Hillbourne | 2 Vantage Way | Poole | BH12 4NU | abilityprojects.***** | 2000 | $31,937,001 | 88 | N/A | N/A | N/A |
| 67 | Adcock Refrigeration And Air Conditioning LIMITED | Unitedkingdom | Chesterton | Cambridge Bus. | Cambridgeshire | CB22 3JH | adcock.***** | 1977 | $31,823,989 | 250 | N/A | N/A | N/A |
| 68 | Box & Charnock LIMITED | Unitedkingdom | Wootton | Unit 15 | Bedford Borough | MK44 3WJ | boxcharnock.***** | 1977 | $31,684,937 | 40 | N/A | N/A | N/A |
| 69 | Express Utilities LIMITED | Unitedkingdom | Harlow | 4 Astra Centre | Essex | CM20 2BN | eplr.***** | 1998 | $31,375,491 | 112 | N/A | N/A | N/A |
| 70 | Grant Store LIMITED | Unitedkingdom | Pennington Green | Unit 20 | Manchester, Greater Manchester | WN2 2PR | grant-store.***** | 2018 | $31,321,049 | 99 | N/A | N/A | N/A |
| 71 | Stonegrove LTD. | Unitedkingdom | Upnor | Unit 3, Boyd Business Centre | Medway | ME2 4DZ | stonegrove.***** | 1975 | $30,767,440 | 43 | N/A | N/A | N/A |
| 72 | Airco Refrigeration And Airconditioning LIMITED | Unitedkingdom | Bransholme | Airco House | City of Kingston-upon-hull | HU3 4DL | airco.***** | 1997 | $30,645,826 | 208 | N/A | N/A | N/A |
| 73 | Warburton Building Services LIMITED | Unitedkingdom | Botley | Chandler House | Oxfordshire | OX2 9NS | warburton.***** | 1979 | $30,412,593 | 142 | N/A | N/A | N/A |
| 74 | Vectaire LIMITED | Unitedkingdom | Hedsor | Lincoln Road | Buckinghamshire | HP12 3RH | vectaire.***** | 1987 | $30,329,193 | 100 | N/A | N/A | N/A |
| 75 | Hotchkiss LTD | Unitedkingdom | Sandiacre | Unit 7a | Derbyshire | NG10 5PQ | hotchkissairsupply.***** | 1967 | $30,182,351 | 119 | N/A | N/A | N/A |
| 76 | Warmup PLC | Unitedkingdom | Harlesden | 702 Tudor Estate Abbey Road | London | NW10 7UW | warmup.***** | 1994 | $30,027,584 | 140 | N/A | N/A | N/A |
| 77 | Petro Gas Llp | Unitedkingdom | Saint Giles | 71-75 Shelton Street | London | WC2H 9JQ | N/A | 2009 | $29,543,341 | 1,354 | N/A | N/A | N/A |
| 78 | J A Brooks Mechanical Services LIMITED | Unitedkingdom | Moorgate | 6th Floor | London | EC2A 2AP | ja-brooks.***** | 1925 | $28,781,823 | 80 | N/A | N/A | N/A |
| 79 | Btu (installation & Maintenance) LIMITED | Unitedkingdom | Guildford | 38 Weyside Road | Surrey | GU1 1JB | btupoolsupplies.***** | 1967 | $28,572,319 | 121 | N/A | N/A | N/A |
| 80 | H & A Mechanical Services LIMITED | Unitedkingdom | Magherafelt | 28 Five Mile Straight | Mid Ulster | BT45 7EG | hamechanicalservices.***** | 1998 | $28,454,228 | 193 | N/A | N/A | N/A |
| 81 | Edmund Services LIMITED | Unitedkingdom | Upminster | 12/13 Saxon House | London | RM14 3PJ | edmundservices.***** | 1984 | $28,294,973 | 118 | N/A | N/A | N/A |
| 82 | Nationwide Air Conditioning LIMITED | Unitedkingdom | Edenbridge | Agusta House | Kent | TN8 6ED | ngukltd.***** | 2001 | $28,256,217 | 131 | N/A | N/A | N/A |
| 83 | Glow Green LIMITED | Unitedkingdom | Red Hill | Avalon | Bournemouth | BH8 8EZ | glowgreenltd.***** | 2011 | $28,249,142 | 131 | N/A | N/A | N/A |
| 84 | Primech Building Services LIMITED | Unitedkingdom | Gillingham | Unit 2 | Medway | ME8 0NJ | primechservices.***** | 2015 | $27,607,652 | 56 | N/A | N/A | N/A |
| 85 | Auger Site Investigations LIMITED | Unitedkingdom | Wallasey | Auger House | Wirral, Merseyside | CH45 8RH | auger.***** | 1995 | $27,442,809 | 89 | N/A | N/A | N/A |
| 86 | Gem Environmental Building Services LIMITED | Unitedkingdom | Saint Johns Wood | Stoneleigh Terrace | London | N19 5TY | gemebs.***** | 1999 | $27,282,881 | 146 | N/A | N/A | N/A |
| 87 | Steve Gregor Plumbing And Heating LIMITED | Unitedkingdom | Bridgeyate | Unit 1 | South Gloucestershire | BS30 5LW | gregorheating.***** | 1999 | $27,082,291 | 118 | N/A | N/A | N/A |
| 88 | Neil Shacklock Plumbing And Heating Contractors LIMITED | Unitedkingdom | Sutton-in-ashfield | Brierley Park Close Shaclock House Brierley Industrial Park | Nottinghamshire | NG17 3FW | shacklocks.***** | 1968 | $26,881,209 | 122 | N/A | N/A | N/A |
| 89 | Hensall Mechanical Services LIMITED | Unitedkingdom | Eggborough | Roall Lane | North Yorkshire | DN14 0NY | hensall.***** | 1978 | $26,803,858 | 101 | N/A | N/A | N/A |
| 90 | M.C.P. Property Group LTD | Unitedkingdom | Hertford Heath | Building B | Hertfordshire | SG13 7NN | wspgroup.***** | 2015 | $26,787,285 | 150 | N/A | N/A | N/A |
| 91 | M.c.p.property Services LIMITED | Unitedkingdom | Hertford Heath | Building B | Hertfordshire | SG13 7NN | mcp.***** | 1999 | $26,787,285 | 150 | N/A | N/A | N/A |
| 92 | Hutcheon Services LIMITED | Unitedkingdom | Charlestown | Bourtree House | Aberdeen City | AB12 3LW | hutcheon.***** | 1975 | $26,630,194 | 172 | N/A | N/A | N/A |
| 93 | Hewer Facilities Management LIMITED | Unitedkingdom | Matson | Unit G1 | Gloucestershire | GL2 2FN | facebook.***** | 1946 | $26,542,992 | 144 | N/A | N/A | N/A |
| 94 | 00604621 LIMITED | Unitedkingdom | Palmersville | Wesley Dr | North Tyneside, Tyne and Wear | NE12 9TN | N/A | 1958 | $26,213,296 | 132 | N/A | N/A | N/A |
| 95 | Thermatic Technical Fm LIMITED | Unitedkingdom | Cadishead | Unit 3 | Manchester, Greater Manchester | M50 3UP | thermatic.***** | 2017 | $26,069,241 | 152 | N/A | N/A | N/A |
| 96 | Mitton Aftercare LIMITED | Unitedkingdom | Esholt | Mackenzie House | Bradford, West Yorkshire | BD12 0HS | mittongroup.***** | 2003 | $25,985,714 | 233 | N/A | N/A | N/A |
| 97 | Woodward & CO (environmental) LIMITED | Unitedkingdom | Tewkesbury | The Courtyard | Gloucestershire | GL20 8GD | woodward.***** | 2004 | $25,673,534 | 23 | N/A | N/A | N/A |
| 98 | Therma-Mech LTD | Unitedkingdom | Bristol | Cargo Work | City of Bristol | BS1 6ZU | N/A | 2013 | $25,248,865 | 84 | N/A | N/A | N/A |
| 99 | Weatherite Air Conditioning LIMITED | Unitedkingdom | West Bromwich | Weatherite House | Sandwell, West Midlands | B70 7JE | weatherite-group.***** | 1984 | $25,177,997 | 135 | N/A | N/A | N/A |
| 100 | Clover Technical Services LIMITED | Unitedkingdom | Birkenhead | Valiant Way | Wirral, Merseyside | CH41 9HS | cloverts.***** | 1991 | $25,166,767 | 92 | N/A | N/A | N/A |