| Alta Capital Limited | London | 2018 |
| Alta Estate Services Limited | Edgbaston | 1989 |
| Altage Ltd | Harrogate | 2022 |
| Altahullion Energy Limited | Kings Langley | 2023 |
| Altaveedan Energy Limited | Belfast | 2015 |
| Altcar Solar Limited | London | 2020 |
| Alten Energy Ltd | London | 2022 |
| Alternate Energies Limited | Norwich | 2011 |
| Alternate Energy Supplies Limited | Rotherham | 2011 |
| Alternative Energy Solutions (Service & Installation) Ltd | Didcot | 2011 |
| Alternative USE Boston Projects (1) Limited | Billericay | 2022 |
| Alternative USE Boston Projects (1)HOLDINGS Limited | Billericay | 2023 |
| Alternative USE Boston Projects (Development) Limited | Billericay | 2026 |
| Alternative USE Boston Projects Holdings Limited | Billericay | 2023 |
| Alternative USE Boston Projects Limited | Loughton | 2017 |
| Alternative USE Limited | Billericay | 2020 |
| Alternative USE Projects Limited | Billericay | 2015 |
| Alternity Biogas Energy Limited | Lisburn | 2015 |
| Altgolan Windfarm Limited | Belfast | 2006 |
| Altherm Ltd | York | 2019 |
| Altiga Limited | | 1947 |
| Altigarron Power Ltd | Belfast | 2012 |
| Altitude LNG Limited | Ruislip, | 2025 |
| Altnabreac Wind Farm Limited | Edinburgh | 2020 |
| Alto Prodotto Wind Limited | London | 2011 |
| Alton Power (2014) Limited | Ashby-De-La-Zouch | 2014 |
| Altrincham-Air Ltd | Altrincham | 2024 |
| Altyre II Windfarm Limited | Edinburgh | 2018 |
| Alva 1 Ltd | Falmouth | 2013 |
| Alvah Energy Ltd. | Peterhead | 2013 |
| Alvechurch Heating & Plumbing Services Limited | Derby | 1973 |
| Alverdiscott Battery Storage Limited | Stonehouse | 2023 |
| Alvolt Energy Ltd | Southampton | 2020 |
| Always Testing Ltd | London | 2019 |
| Alzra Ltd | Liverpool | 2026 |
| AM Air Conditioning (UK) Limited | Woodford Green | 2007 |
| AM Fast Construction Ltd | London | 2025 |
| AM GAS & Electrical Services Ltd | London | 2022 |
| Am.Tec Electrical Services Limited | Middlesex | 1997 |
| AMA Electrical Ltd. | Lincoln | 2011 |
| Amae Electrical Services Ltd | Altrincham | 2015 |
| Amalgamated Smart Metering Limited | Nottingham | 2014 |
| Amantien Electrical Services Ltd | Wembley | 2015 |
| Amaryllis Energy Ltd | Newcastle Upon Tyne | 2026 |
| Amatol Air Ltd | London | 2021 |
| Ambassador Energy (Gartloss) Limited | Glasgow | 2023 |
| Ambassador Energy Solutions Limited | Glasgow | 2022 |
| Amber Energy Storage (Projectco Two) Limited | London | 2017 |
| Amber Fusion (Luton) Limited | London | 2022 |
| Amber Fusion Limited | London | 2014 |
| Amber Green Victus (Dufless) Limited | Belfast | 2020 |
| Amber Powervale Limited | Morpeth | 2020 |
| Amber REI Green Energy Limited | Birmingham | 2011 |
| Amber Solar Parks (Holdings) Limited | London | 2012 |
| Amber Solar Parks Limited | London | 2012 |
| Amber Solar Power Limited | London | 2021 |
| Amberside Power Ltd | Hemel Hempstead | 2017 |
| Ambient Environmental Solutions Ltd | Carshalton | 1997 |
| Ambition Community Energy C.I.C. | Bristol | 2018 |
| Ambrose Spence Consulting Ltd | Taunton | 2022 |
| AMC Electrical Contractors Limited | Watford | 2008 |
| Amcy Marketing Solutions Ltd | Ashton-Under-Lyne | 2020 |
| AMD Property Installations Ltd | Manchester | 2026 |
| Amec Construction Ltd | Bradford | 2023 |
| Amegni Limited | Caersws | 2007 |
| Amegni Renewables Limited | Powys | 2006 |
| Amesbury Renewable Energy Ltd | London | 2002 |
| Amessai Energy Research Limited | London | 2022 |
| Amethyst Marine Services Limited | Bristol | 1972 |
| Amey MAP Services Limited | Westcliff-On-Sea | 2017 |
| AMG Electrical Solutions Limited | Hornchurch | 2012 |
| AMG Energy North East Limited | Durham | 2024 |
| AMG Power Limited | Durham | 2024 |
| AMH Air Conditioning (South West) Limited | Weston-Super-Mare | 2007 |
| Amicare Solar Limited | Leicester | 2022 |
| Amicus Renewables Limited | Milton Keynes | 2015 |
| Aminth Energy Ltd | Rotherham | 2017 |
| AMJ Jointing Ltd | Portsmouth | 2021 |
| Amma Management Limited | Ilkeston | 2011 |
| Ammonite Carbon Storage Ltd | London | 2024 |
| AMP Biomass (NET Zero 1) Limited | London | 2021 |
| AMP Biomass (NET Zero 2) Limited | London | 2021 |
| AMP GM 003 Limited | London | 2013 |
| AMP GM001 Limited | London | 2013 |
| AMP GM004 Limited | London | 2014 |
| AMP GM005 Limited | London | 2012 |
| AMP GM006 Limited | London | 2014 |
| AMP GM007 Limited | London | 2015 |
| AMP GM011 Limited | London | 2013 |
| AMP GM012 Limited | London | 2015 |
| AMP GM016 Limited | London | 2014 |
| AMP GM024 Limited | London | 2015 |
| AMP HA001 Limited | London | 2014 |
| AMP HA004 Limited | London | 2015 |
| AMP HA005 Limited | London | 2015 |
| AMP HA006 Limited | London | 2015 |
| AMP HA008 Limited | London | 2015 |
| AMP HA010 Limited | London | 2015 |
| AMP Hydrogen 2 Limited | London | 2022 |
| AMP Hydrogen 3 Limited | London | 2024 |