| ACO (Bath) Limited | Bath | 2014 |
| Acorn Peach Energy Ltd. | Milton Keynes | 2016 |
| Acorn Power Limited | London | 2020 |
| Acorn Renewables Ltd | Watford | 2021 |
| Acornfields UK Limited | London | 2022 |
| ACP (Scot Wind) Ltd | London | 2018 |
| ACP (Wind Farm) Ltd | London | 2018 |
| ACP Solar Limited | London | 2017 |
| ACP WNI Limited | Belfast | 2016 |
| ACR Energy Ltd | London | 2010 |
| Acre Energy Limited | Faversham | 2013 |
| Acreback Road Energy Limited | Hillsborough | 2025 |
| ACS Biomass Ltd | Stirling | 2011 |
| Acsim Group Ltd | Bognor Regis | 2016 |
| Action Airconditioning Limited | Cardiff | 1996 |
| Action Electrical Contractors Limited | Cwmbran | 2010 |
| Activa Process Management Green Projects Ltd | London | 2020 |
| Activa Process Management Limited | London | 2026 |
| Active Air Conditioning Limited | Stirling | 1999 |
| Active Air Engineering Ltd | Watford | 2024 |
| Active Electrical Solutions (York) Ltd | York | 2009 |
| Active Heat Ltd | London | 2026 |
| Active Heat Midlands Ltd | Birmingham | 2023 |
| Active Powwr Ltd | Southampton | 2024 |
| Activepure Air UK Ltd | Ampthill | 2022 |
| Actrees Solar Power Limited | Faversham | 2015 |
| Acumen Technical Solutions Limited | Flintshire | 2005 |
| Acute Solutions U.K. Limited | Prescot | 2000 |
| Acutus Energy Limited | Wadhurst | 2019 |
| AD Bioenergy Cornwall Limited | Manchester | 2015 |
| AD Bioenergy Holdings Limited | Manchester | 2015 |
| AD Chester Limited | Maidstone | 2015 |
| AD Electricity Ltd | Armagh | 2017 |
| AD Installations & Contracting Limited | Maidstone | 2010 |
| Adal Electrical Limited | Doncaster | 2026 |
| Adalinda Solar SPV 1 Limited | London | 2012 |
| Adamson DEL 27 Limited | Salford Quays | 2023 |
| Adcock Farming Limited | Shawbury | 2014 |
| Adcon Hvac Limited | Portsmouth | 2021 |
| Addfrost Maintenance Services Limited | Solihull | 1998 |
| Addison Energy Limited | London | 2012 |
| Addisons Solar and Renewables Limited | Thirsk | 2026 |
| ADE North East Limited | South Shields | 2020 |
| Adekofo Ltd | Luton | 2016 |
| Adelie Energy Ltd | Ravenglass | 2022 |
| Adey Commissioning Services Ltd | Honiton | 2024 |
| ADF Wind Ltd | Newcastle Upon Tyne | 2021 |
| ADH AD Limited | Dumfries | 2016 |
| ADH Solutions Limited | Norwich | 2021 |
| Adhara Solar Ltd | Bristol | 2020 |
| ADI Green Energy Limited | Airdrie | 2018 |
| Adjacent Power Limited | Woking | 2012 |
| ADL Heating and Cooling Solutions Ltd | Colchester | 2022 |
| Adler Cooling Ltd | London | 2016 |
| Adlite Electrical Services Ltd | Brighton | 2024 |
| Adolf Chailaite Shelby Ltd | London | 2020 |
| Adons Limited | | 2005 |
| Adrian Francis Associates Ltd | Altrincham | 2002 |
| Adrians Electrical Services Limited | Wolverhampton | 2015 |
| Adriatic Green Energy Ltd | London | 2020 |
| Adriatic Power Production Limited | London | 2015 |
| ADS Airconditioning Ltd | Ashton-Under-Lyne | 2024 |
| ADS Cooling Ltd | Southampton | 2006 |
| Adsnewton Ltd | Morden | 2018 |
| Adtek Limited | Newcastle Upon Tyne | 2012 |
| ADV 001 Limited | Nottingham | 2019 |
| ADV 003 Limited | London | 2019 |
| ADV 004 Limited | London | 2019 |
| ADV 005 Limited | London | 2019 |
| ADV 006 Limited | London | 2019 |
| Advance AC Mechanical Ltd | Nottingham | 2024 |
| Advance Air Conditioning Ltd | Nottingham | 2015 |
| Advance Energy Limited | Ballyclare | 2022 |
| Advance Grid Solutions Limited | Bellshill | 2022 |
| Advanced Building Technology (N E) Ltd | Seaham | 2006 |
| Advanced Climate Technical Services Ltd. | Tadley | 2018 |
| Advanced Cooling Southern Limited | Waterlooville | 2022 |
| Advanced Electricity Networks Limited | Braintree | 2023 |
| Advanced Energy Solution Ltd | London | 2014 |
| Advanced Energy Storage Ltd | Kettering | 2022 |
| Advanced Fuel Plants Limited | London | 2023 |
| Advanced GAS & Power Ltd | Sunderland | 2023 |
| Advanced Generation Fairwood Lakes Limited | Coventry | 2025 |
| Advanced Recycling Thornton Limited | Fleetwood | 2024 |
| Advanced Renewable Power Ltd | Washington | 2011 |
| Advantage Air Systems Limited | Horsham | 1994 |
| Advantage Utilities Limited | Weybridge | 2001 |
| Advantix Automation Solutions Limited | Plymouth | 2016 |
| Advent Biogas Limited | Ballymena | 2018 |
| Advent Energy and Technology Limited | Banbridge | 2022 |
| Advent Wind Banbridge Limited | Ballymena | 2013 |
| Advent Wind Energy Limited | Newry | 2014 |
| Advent Wind Ltd | Newry | 2010 |
| Advent.Re Ltd | Thame | 2017 |
| Advica Holdings Limited | Wokingham | 2016 |
| Ady&Cory Manchester Construction&Electrical Services Ltd | Manchester | 2026 |
| AE Energy Ltd | Chester | 2023 |
| AEE Renewables UK 13 Limited | London | 2010 |
| AEE Renewables UK 15 Limited | London | 2010 |
| AEE Renewables UK 16 Limited | London | 2010 |