| AGR Solar Holdco Limited | London | 2019 |
| AGR Solar Midco Limited | London | 2022 |
| Agri-Gen Limited | Woodbridge | 2008 |
| Agricultural and Mobile Airconditioning Limited | Nailsworth | 1990 |
| Agricultural Solar Investments Limited | Ballycastle | 2013 |
| Agrigen Power Ltd | Inverness | 2025 |
| AGS Cooling System and Industrial Kitchen Ltd | Enfield | 2023 |
| AGS Covenhill Ltd | Bellshill | 2023 |
| AGS Harestonhill Ltd | Bellshill | 2023 |
| AGS Inverclyde Ltd | Bellshill | 2023 |
| AGS Langlands Gate Ltd | Bellshill | 2024 |
| AGS Meadowhead Ltd | Bellshill | 2023 |
| AGU (NE) Limited | Durham | 2026 |
| AGV (Annesborough) Limited | Belfast | 2018 |
| AGV (Craigavon) Limited | Belfast | 2017 |
| AGV Dufless Limited | Belfast | 2023 |
| AGV Energy Limited | Belfast | 2023 |
| AGV Stoke Ltd | Stoke-On-Trent | 2023 |
| AH Farm Energy Services Ltd | Craven Arms | 2026 |
| AH Services (Kent) Limited | Sittingbourne | 2007 |
| AHM Electrical Ltd | Derby | 2023 |
| AHO Solar Ltd | Bradford | 2023 |
| AI Data Center Power Ltd | London | 2025 |
| AIC Energy Limited | Armagh | 2021 |
| Aiden Digital Labs Ltd | London | 2022 |
| Aidien Limited | London | 2023 |
| AIK2A Sustainable Energy (Holdings) Ltd | Aberdeen | 2023 |
| AIK2A Sustainable Energy Ltd | Aberdeen | 2014 |
| Aikengall Community Wind Company Limited | Edinburgh | 2006 |
| Aikengall II Community Wind Company (Holdings) Limited | Edinburgh | 2013 |
| Aikengall II Community Wind Company Limited | Edinburgh | 2013 |
| Ailside Removals Limited | London | 2026 |
| Ainderby Solar Farm Limited | London | 2015 |
| Aintree Cooling Limited | Liverpool | 2020 |
| Air & Renewable Resources Limited | Aberdeen | 2014 |
| Air 27 Air Conditioning Installation London Ltd | Nottingham | 2026 |
| Air Assist Ltd | Birmingham | 2024 |
| Air Balancing Commissioning Services Limited | Cheshire | 1989 |
| Air Care Refrigeration Ltd | London | 2011 |
| Air Clima-Comfort Ltd | London | 2022 |
| Air Climate Ltd | Rotherham | 2020 |
| Air Climate Solutions Limited | Ayr | 2015 |
| Air Compliance Ltd | Stourport-On-Severn | 2024 |
| Air CON Environmental Limited | Camberley | 2009 |
| Air CON Essex Limited | Clacton-On-Sea | 2022 |
| Air CON Mike Limited | Addlestone | 2025 |
| Air Conditioning & Environmental Services Limited | Aylesbury | 2002 |
| Air Conditioning & Refrigeration Aircare Limited | Maldon | 2003 |
| Air Conditioning & Refrigeration Ltd | Alton | 2025 |
| Air Conditioning & Refrigeration Services (Newcastle) Limited | Newcastle Upon Tyne | 1979 |
| Air Conditioning Advance Limited | London | 2022 |
| Air Conditioning and Electrical Limited | Stratford-Upon-Avon | 2004 |
| Air Conditioning Bristol Ltd | Bristol | 2013 |
| Air Conditioning Installation and Maintenance Ltd | Greenhithe | 2013 |
| Air Conditioning Installations UK Limited | Daventry | 2011 |
| Air Conditioning Projects Limited | Barnet | 2008 |
| Air Conditioning Scotland Limited | Shotts | 2015 |
| Air Conditioning Shop Online Limited | Ilford | 2023 |
| Air Conditioning Swansea Limited | Llanelli | 2013 |
| Air Conditioning World Limited | Bolton | 2025 |
| Air Cool Engineering Service & Maintenance Ltd. | Aston | 1993 |
| Air Core EV Ltd | Belfast | 2020 |
| Air Core Limited | Belfast | 2010 |
| Air Corps Air Conditioning Ltd | Tunbridge Wells | 2022 |
| Air Corre Ltd | Belfast | 2020 |
| Air Duct Solutions Ltd | Christchurch | 2014 |
| Air Engineering Solutions Limited | Wednesbury | 1999 |
| Air Force Renewable Energies Ltd | London | 2023 |
| Air Liquide Advanced Business and Technologies UK Limited | Birmingham | 2013 |
| Air on Services Ltd | Stockport | 2017 |
| Air Pack Mechanical Ltd | Gravesend | 2017 |
| Air Performance Ltd | Waterlooville | 2018 |
| Air Products Renewable Energy Limited | Chertsey | 2013 |
| Air Revolution Ltd | Lewes | 2026 |
| Air River Limited | Magherafelt | 2011 |
| Air Source Air Conditioning Ltd | Cranbrook | 2025 |
| Air Source Heat Pumps Ltd | Hastings | 2018 |
| Air Supply Ventilation Ltd | Galashiels | 2014 |
| Air Swift Ltd | Wisbech | 2021 |
| Air Tech AC Limited | Belvedere | 2018 |
| Air Tech Cooling Ltd | Leigh-On-Sea | 2024 |
| Air Works UK Limited | Godalming | 2002 |
| Air-Con Crazy Ltd | Leigh-On-Sea | 2025 |
| Air-Con Service Limited | Ilford | 2003 |
| Air-Con Supply Ltd. | London | 2015 |
| Air-Conditioning Refrigeration Technologies Limited | Bury St Edmunds | 2019 |
| Air-On Tech Ltd | London | 2022 |
| Air-Ref Limited | Woking | 1998 |
| Aircareserviceselectrical Limited | Aldershot | 2017 |
| Airco Solutions Ltd | London | 2025 |
| Aircomm Ventilation Limited | London | 2018 |
| Aircon Art Ltd | Redhill | 2022 |
| Aircon Repair Ltd | Tonbridge | 2026 |
| AIRCON4HOME Limited | Feckenham | 2021 |
| Airconco (UK) Limited | Mill Hill East | 1998 |
| Aircono Ltd | London | 2014 |
| Airconomy Ltd | Hornchurch | 2024 |
| Airconuk Ltd | London | 2024 |
| Aircraft Services and Parts Limited | Bolney Haywards Heath | 1986 |
| Airedale Energy Limited | Goole | 2014 |