| Airficiency Ltd | Redhill | 2025 |
| Airfield Wind Farm Limited | London | 2015 |
| Airflow Containment Services Ltd | Benfleet | 2022 |
| Airgen Limited | Sevenoaks | 1999 |
| Airheat Ltd | Worcester | 2010 |
| Airies Windfarm Limited | Aberdeen | 2011 |
| Airlec Solutions Limited | Colchester | 2014 |
| Airmac UK Ltd | Nottingham | 2014 |
| Airnex Climate Solutions Ltd | Brighton | 2026 |
| Airo Supply Limited | Aldershot | 2025 |
| Airomax Ltd | London | 2025 |
| Aironex Ltd | Beckenham | 2021 |
| Airox Ltd | London | 2018 |
| Airpro UK Limited | Hinckley | 2004 |
| Airsistance Ltd | Glossop | 2025 |
| Airsolutions-Nw Limited | Ormskirk | 2015 |
| Airsource Climate Ltd | Alton | 2020 |
| Airtana Limited | Dromore | 2015 |
| Airtec Cooling Solutions Ltd | Dromore | 2024 |
| Airtech UK Limited | Sutton Coldfield | 1988 |
| Airtech Vehicle Air Conditioning and Heating Ltd | Northampton | 2024 |
| Airtek Airconditioning & Technical Services Limited | Timperley | 2003 |
| Airtek Solutions Ltd | Derby | 2025 |
| Airtemp Control Limited | Telford | 2008 |
| Airtricity Ltd | Bedford | 2026 |
| Airvac Ltd. | North Cheam | 2015 |
| Airwave Air Conditioning Ltd | Sutton-In-Ashfield | 2020 |
| Airwaves Air Conditioning Limited | Peterborough | 2017 |
| Airway Limited | Sheffield | 2004 |
| Airways AC Ltd | Chelmsford | 2023 |
| Airy Air Conditioning Ltd | Chelmsford | 2024 |
| Aisling Renewables Ltd | Bristol | 2019 |
| Aitechgreen Ltd | Norwich | 2026 |
| Aitkenhead Storage Facility Limited | Manchester | 2023 |
| AJ AC Northwest Ltd | Liverpool | 2021 |
| AJ Fraser Services Limited | Fareham | 2007 |
| AJ Jointing Services Ltd | Halifax | 2023 |
| AJ Systems and Services Ltd | Chilcompton | 2017 |
| AJ Technical Services Ltd | Barking | 2026 |
| AJ Wilson Plumbing & Heating Ltd | Durham | 2006 |
| AJ Wind Ltd | Wallsend | 2024 |
| Ajar Energy Solutions Ltd | Brentford | 2025 |
| Ajax Hvac Ltd | Sawbridgeworth | 2021 |
| AJC Energy Limited | Port Talbot | 2021 |
| Ajet Engineering Consultancy Limited | Watford | 2019 |
| AJH Electrical Services Ltd | Macclesfield | 2011 |
| AJH Energy Limited | Stockton-On-Tees | 2014 |
| AJL Licenced Ltd | Bournemouth | 2023 |
| AJL Utilities Limited | Newton Aycliffe | 2025 |
| AJM Utilities Ltd | Poole | 2018 |
| Ajooni a Ltd | Ruislip, | 2026 |
| AJP Heating Solutions Ltd | Bolton | 2026 |
| AJS Ignite Ltd | Truro | 2024 |
| AJT Cooling Ltd | Wigston | 2020 |
| AJW Energy Limited | Guildford | 2013 |
| AK Cooling Solutions Limited | Wickford | 2025 |
| AK Renewable Energy (Akre) UK Ltd | London | 2026 |
| AK Utilities Ltd | Glasgow | 2022 |
| AKA Mechanical Ltd | Swadlincote | 2015 |
| AKA Sparks Electrical Contractors Limited | London | 2016 |
| Akeman Solar Park Limited | Shepton Mallet | 2019 |
| Aker Offshore Wind Limited | Aberdeen | 2021 |
| Akereos Commodities Ltd | London | 2024 |
| Akku Energy Limited | Cupar | 2022 |
| Akoni Renewables UK Ltd | Oxford | 2026 |
| AKP Installations Ltd | Chester | 2019 |
| Aktekk Energy and Power Engineering Limited | Liverpool | 2014 |
| AKV Energy Ltd | Belfast | 2014 |
| AL Amoodi Holdings Ltd | Bury St. Edmunds | 2025 |
| AL Boum Photo Ltd | London | 2020 |
| AL Malik Ittehad Trading Ltd | London | 2026 |
| AL Power Ltd | King'S Lynn | 2014 |
| Al-Raebi for Trading Ltd | Birmingham | 2026 |
| Al-Suwaihra Flowers for Trade and Investment Ltd | London | 2025 |
| Alacor Electrical Ltd | Stourbridge | 2018 |
| Aladdin Green Energy Co. Limited | Cardiff | 2020 |
| Alam & SON Plumbing & Heating Specialists Ltd | Bradford | 2022 |
| Alan Energy Limited | Hamilton | 2014 |
| Alan Millman Electrics Ltd | South Molton | 2020 |
| Alan Waddell Electrical Limited | Glasgow | 2019 |
| Alauna Renewable Energy Limited | Bedford | 2011 |
| ALB Solars Ltd | Gillingham | 2025 |
| Alban Energy Limited | Glasgow | 2017 |
| Albatern Limited | Roslin | 2010 |
| Albion HV Services Limited | Cardiff | 2016 |
| Albion Solar Limited | London | 2011 |
| Alboro Energy Ltd | Cambridge | 2019 |
| Albrighton Battery Storage Limited | Bristol | 2023 |
| Albrighton Solar Farm Ltd | London | 2014 |
| Alcemi Energy Limited | Lingfield | 2019 |
| Alcemi Storage Developments 1 Limited | London | 2019 |
| Alcemi Storage Developments 2 Limited | London | 2019 |
| Alcemi Storage Developments 23 Limited | London | 2023 |
| Alcemi Storage Developments 3 Limited | Rotherham | 2019 |
| Alcemi Storage Developments 4 Limited | Rotherham | 2019 |
| Alcemi Storage Developments 5 Limited | London | 2019 |
| Alcemi Storage Developments 6 Limited | Rotherham | 2022 |
| Alcemi Storage Developments 7 Limited | London | 2022 |
| Alcemi Storage Developments 8 Limited | London | 2022 |
| Alcool Air Conditioning Ltd | Hull | 2010 |