| Avanti Grid Limited | Salford | 2021 |
| Avanti-E Limited | Bude | 2022 |
| Avantigas on Ltd | Chesterfield | 2016 |
| AVC Mechanical Ltd | Birkenshaw | 2018 |
| AVC Solar Ltd | Basildon | 2023 |
| AVE 002 Limited | London | 2018 |
| Avenue Solar Farm Limited | London | 2011 |
| Averill Farm Limited | London | 2014 |
| Avesi Limited | London | 2010 |
| Aveum Technologies Ltd | London | 2026 |
| AVH Solar Limited | Huntingdon | 2022 |
| Avis Energy Limited | London | 2011 |
| Avocado High Tech Limited | London | 2025 |
| Avocet Renewables Limited | Tiverton | 2014 |
| Avodah Renewable Energies Ltd | Hillsborough | 2013 |
| Avon Biofuel Plant Limited | London | 2026 |
| Avon Umbra Limited | Morpeth | 2020 |
| Avonaire Ltd | Bristol | 2002 |
| Avoncliff Hydropower Ltd | Bradford-On-Avon | 2017 |
| Avonmouth Advanced Fuel Limited | London | 2026 |
| Avonmouth Advanced Fuel Plant Holdings Limited | London | 2026 |
| Avonmouth Battery Storage Limited | Bristol | 2024 |
| Avonmouth Generation Limited | Greenock | 2017 |
| Avonmouth Land Holdings Limited | London | 2026 |
| Avonmouth Windfarm Limited | Berkeley | 2013 |
| AVS Mining Ltd | Poole | 2025 |
| AW1 Energy Storage Limited | Nash | 2020 |
| AW2 Energy Storage Limited | Nash | 2025 |
| AW5 Storage Holdings Limited | Edinburgh | 2025 |
| Awasiri Ltd | London | 2022 |
| Awch Group Limited | Camberley | 2024 |
| AWD Air Conditioning Ltd | Maidstone | 2015 |
| AWE Renewables Limited | Leighton Buzzard | 2013 |
| AWE Services Ltd | Whitstable | 2018 |
| Awel Newydd CYF | London | 2005 |
| Awel Y Gwrhyd C.I.C. | Ammanford | 2011 |
| Awelon CYF | Llandudno | 2016 |
| AWG Air Conditioning Ltd | Hertfordshire | 2017 |
| AWH Electrical Limited | Bromborough | 2018 |
| Awjf Limited | Peterhead | 2012 |
| AWL Commercial GAS Limited | Colchester | 2016 |
| AWO Energy Limited | Ramsey | 2015 |
| AWP Wind 1 Ltd | Malton | 2020 |
| AWP Wind 2 Limited | Malton | 2021 |
| AWP Wind 3 Limited | Malton | 2021 |
| Awyrgwyrdd(Greenair) Ltd | Port Talbot | 2019 |
| AXA Engineering Ltd | London | 2016 |
| AXA Power Limited | Chorley | 2019 |
| Axen Business House (UK) Limited | Ilford | 2026 |
| Axim Energy Limited | Isleworth | 2011 |
| Axion Terra Ltd | Glasgow | 2026 |
| Axionaire Ltd | London | 2024 |
| Axis Mundi Ltd | Biggleswade | 2017 |
| Axminster Energy and Utilities Group Limited | Axminster | 2022 |
| Axpo UK Limited | London | 2008 |
| Ayanda UK Ltd | Great Chesterford | 2018 |
| Aycliffe Solar Limited | London | 2021 |
| Aylesbury Air Conditioning Limited | Aylesbury | 2002 |
| AYR Flexpower Limited | Aberdeen | 2024 |
| Ayrenergy Limited | Orkney | 2009 |
| Ayrshire Chip 'N' Logs Limited | Mauchline | 2016 |
| Aysgarth Falls Hydro-Electric Company Limited | Barnard Castle | 2008 |
| Ayshford Solar (Holding) Limited | London | 2012 |
| AZ Heat Limited | Middlesbrough | 2023 |
| AZI GAS Services Limited | Milton Keynes | 2024 |
| Azores Energy Limited | London | 2017 |
| Azrum Ltd | Wick | 2022 |
| B & B Air Conditioning & Refrigeration Ltd | Houghton Le Spring | 2003 |
| B & D Energy Limited | Barking | 2016 |
| B & I Estates Limited | Newcastle Upon Tyne | 2013 |
| B & J Mechanical Services Limited | Weston-Super-Mare | 2013 |
| B Boyle Electrics Ltd | Omagh | 2023 |
| B F Energy Limited | Roslin | 2018 |
| B G Utilities Limited | Ramsgate | 2022 |
| B H Heating Limited | Romsey | 2010 |
| B J Moran (Electrical Services) Ltd | Windermere | 2004 |
| B K S Energy Limited | Kings Langley | 2010 |
| B O Hurt Ltd | Liverpool | 2026 |
| B R Wood & Co Limited | Driffield | 2022 |
| B T Electrics Limited | Middlesex | 2007 |
| B T I Concept Ltd | London | 2020 |
| B&M S4U Limited | Huntingdon | 2018 |
| B&N Air Conditioning Ltd | Pinner | 2023 |
| B&N Refrigeration & Airconditioning Limited | Middlesex | 2003 |
| B-Cool Coldroom and Ai̇rcondi̇ti̇oni̇ng Ltd | London | 2021 |
| B-Rings Ltd | London | 2020 |
| B. Smith Utilities Limited | London | 2011 |
| B. T. U. Engineering Company Limited | Wirral | 2003 |
| B. Winfieldale & Sons Limited | Swadlincote | 2000 |
| B.N.S. Electrical Services Ltd | Sevenoaks | 2007 |
| B.P. Property Developments Limited | Bury | 1998 |
| B17 Solar Farm Limited | London | 2020 |
| B2B Experts Ltd | Cardiff | 2019 |
| B2B Utilites Ltd | Wokingham | 2019 |
| B9 Energy Control Ltd | Larne | 2008 |
| B9 Energy Horizons Ltd | Larne | 2019 |
| B9 GAS Limited | Larne | 2019 |
| B9 Heat and Power Limited | Larne | 2013 |
| B9 LFG Craigmore Ltd | Larne | 2023 |
| B9 Power Limited | Larne | 2018 |