| A One Jointing Services Ltd | Glasgow | 2026 |
| A One Jointing Systems Limited | East Kilbride | 2005 |
| A P Cook Electrical Limited | Harrogate | 2013 |
| A R GAS Engineers Limited | London | 2017 |
| A Ramsden Holdco Limited | London | 2026 |
| A Sewter Electrical Limited | Lynch Wood, Peterborough | 2009 |
| A Shade Greener (F2) Ltd | London | 2011 |
| A Shade Greener Limited | Tankersley | 2009 |
| A Star Air Conditioning Ltd | Greenford | 2022 |
| A Team ACS Limited | Leicester | 2017 |
| A Thawley GAS Services Limited | Barnsley | 2015 |
| A Wymark Electrical Limited | Swadlincote | 2013 |
| A&B Commissioning Ltd | Ashford | 2019 |
| A&G Airconditioning Ltd | Reading | 2022 |
| A&J Airconditioning & Heating Ltd | Bournemouth | 2022 |
| A&J Cooling Limited | Fleet | 2019 |
| A&M GAS Engineering Ltd | Leicester | 2019 |
| A&N Electric Limited | Orpington | 2025 |
| A&P Tyne (2004) | | 1995 |
| A&R Power Limited | Londonderry | 2013 |
| A&S Power Engineering Consultancy Ltd | Prestatyn | 2025 |
| A&V Renewables Limited | Huntly | 2012 |
| A'Chruach Extension Wind Farm Limited | Milnthorpe | 2014 |
| A'Chruach Phase 2 Wind Farm Limited | Milnthorpe | 2012 |
| A+ Building Services Limited | London | 2007 |
| A-S Solar SPV1 Limited | Chorley | 2025 |
| A-Spec-Gas Services Ltd | Sudbury | 2007 |
| A-Star (South) Limited | Wimborne | 2014 |
| A-Z Energy Solutions Limited | London | 2022 |
| A-Z-Electricallondon. Limited | South Croydon | 2016 |
| A. Scullin Electrics Ltd | Cookstown | 2019 |
| A. Wade Electrical Limited | Poulton-Le-Fylde | 2018 |
| A.A. Mcguckian Limited | Ballymena, | 1936 |
| A.C. Powerlines Ltd | Craigavon | 1999 |
| A.C.J. Trading Limited | Belfast | 2003 |
| A.C.M. (Yorkshire) Limited | Leeds | 2013 |
| A.C.R.C. Limited | Wigston | 1991 |
| A.C.V.R. Services Limited | Birstall | 1982 |
| A.Electrical Services Ltd | London | 2015 |
| A.F.R Pipelines Ltd | Durham | 2020 |
| A.F.S. Property Services Ltd. | Glasgow | 2003 |
| A.G.A. Cooling Ltd. | Tamworth | 2015 |
| A.G.S.S. NI Limited | Belfast | 2023 |
| A.Holroyd Ltd. | Sheffield | 2018 |
| A.K.S. Air Conditioning (Holdings) Limited | Liverpool | 2023 |
| A.M. Services (Edinburgh) Ltd | Prestonpans | 2016 |
| A.M.M GAS Heating & Services Ltd | Erith | 2024 |
| A.R.C. Building Management Facilities Limited | Stoke Plymouth | 2003 |
| A.R.M Electrical Ltd | Bristol | 2021 |
| A.R.M GAS Services Limited | Gravesend | 2013 |
| A.S. Electrical (Southern) Ltd | Carshalton | 2007 |
| A.Salt Power & GAS Ltd | Hull | 2024 |
| A.T.M Elec Ltd | London | 2026 |
| A.T.M. Electrical Services Ltd. | Ryde | 1996 |
| A/C Systems Limited | Epsom | 2012 |
| A1 Aircon Limited | New Milton | 2023 |
| A1 Electrics@Work Limited | London | 2014 |
| A1PLUMBING.RUTLAND Ltd | Oakham | 2018 |
| A2B Energy Solutions Ltd | Banbridge | 2022 |
| A2B GAS Services Ltd | Borehamwood | 2020 |
| A2B Plumbing, Heating & GAS Repairs Ltd | Wigston | 2012 |
| A4-TECH Limited | Edinburgh | 2026 |
| A7 Draffan Limited | Poole | 2010 |
| A7 Greendykeside Limited | Poole | 2005 |
| A7 Lochhead Limited | Poole | 2006 |
| AA Contract Investments Ltd | Glasgow | 2019 |
| AA Energies Ltd | Hayes | 2020 |
| AA Marketing Services Ltd | Walsall | 2023 |
| AA Marsh Electrics Ltd | Herne Bay | 2024 |
| AA Merchant Service Ltd | London | 2022 |
| AA NAT GAS Ltd | Maidenhead | 2023 |
| AAA GAS Energy Solutions Ltd. | Glasgow | 2022 |
| Aaac Limited | Colchester | 2005 |
| AAC Electrical Ltd | Tilbury | 2016 |
| AAC Mechanical Services Limited | Cranbrook | 2013 |
| Aacables Limited | Hartlepool | 2020 |
| Aadhiran Wholesale Ltd | Ilford | 2024 |
| Aairecool Technical Services Limited | Edinburgh | 1991 |
| Aak.G.K Supplies Ltd | London | 2023 |
| Aalborg Energy Technology UK Limited | London | 2022 |
| Aashman Power Limited | Bristol | 2010 |
| Aasv Heating and Plumbing Ltd | Harrow | 2024 |
| AB Air Conditioning Ltd | Burntwood | 2026 |
| AB Air Conditioning Services Ltd | Sutton Coldfield | 2025 |
| AB Cooling Solutions & Shopfitters Ltd | London | 2024 |
| AB Electrical Domestic & Commercial Limited | Matlock | 2011 |
| AB Global Wind Ltd | Barnsley | 2018 |
| AB Tetrawatts Limited | Southall | 2023 |
| ABA Stronalva Limited | Alton | 2007 |
| Abacus Air Conditioning Ltd | Brentwood | 2018 |
| Abbey Ecosse Limited | Forss By Thurso | 2014 |
| Abbey Electrical (Swindon) Limited | Swindon | 2012 |
| Abbey Electrical Services (Hull) Ltd | Hull | 2011 |
| Abbey Energy Limited | Cannock | 2014 |
| Abbey Power Generation Limited | Stamford | 2010 |
| Abbey Power Group Ltd | Stamford | 2016 |
| Abbey Power Reserve Balderton Ltd | Stamford | 2022 |
| Abbey Power Solutions Limited | Stamford | 2011 |
| Abbey Solar Renewables Limited | Halesowen | 2013 |
| Abbeyfields Solar Limited | London | 2015 |