| Atlas Electrical Services Ltd | Looe | 2019 |
| Atlas Energy Solutions Limited | Liverpool | 2025 |
| Atlas Green Energy Limited | Fareham | 2021 |
| Atlas Meridian Energy Ltd | London | 2026 |
| Atlas Power & Industrial Services Limited | Godaming | 2022 |
| Atmos Cool Ltd | London | 2023 |
| Atmosclear Building Services Limited | Paddock Wood | 2003 |
| Atmosfuture Limited | London | 2018 |
| Atomic Electrical Services Limited | St Albans | 2011 |
| Atomic Supplies Ltd | Mirfield | 1995 |
| Aton Energy Development (Northfleet) Limited | London | 2023 |
| Aton Energy Development (Sundon) Limited | London | 2019 |
| Aton Energy ESS 1 Limited | London | 2015 |
| Atreides Wind Services Ltd | Dunoon | 2023 |
| ATS GAS & Heating Ltd | Dumbarton | 2025 |
| ATS Mechanical Services Limited | High Wycombe | 2014 |
| Attadale Grid Limited | Kendal | 2016 |
| Attesta Energy Limited | London | 2026 |
| Attleborough AD Plant Limited | Ely | 2018 |
| Attleborough Eco Electric Limited | Ely | 2004 |
| Attwood Services Limited | Upminster | 2009 |
| ATY Infrastructure Ltd | London | 2023 |
| Auchencarroch Energy Limited | Edinburgh | 1999 |
| Auchenvey WF Limited | Motherwell | 2013 |
| Auchinderran Wind Ltd | Turriff | 2023 |
| Auchnotroch Wind Energy Ltd. | Kirkfieldbank | 2012 |
| Auchren Wind Farm Limited | Edinburgh | 2012 |
| Auchrobert Wind Energy Limited | Edinburgh | 2014 |
| Aughnaglea Energy Limited | Omagh | 2015 |
| Aughnagurgan Wind Farms Limited | Keady | 2013 |
| Augustin Services Limited | Nelson | 2017 |
| Aukera UK 1 Limited | London | 2024 |
| Aukera UK 2 Limited | London | 2024 |
| Aukera UK 3 Limited | London | 2026 |
| Aukera UK Limited | London | 2021 |
| Auquhirie Land Company Limited | Edinburgh | 2006 |
| Aura Air Solutions Ltd | London | 2025 |
| Aura Grid Energy Ltd | Kingston Upon Thames | 2026 |
| Aura Hvac Limited | London | 2019 |
| Aura Nominees Limited | Bristol | 2023 |
| Aura Power Solar UK 1 Ltd | Bristol | 2019 |
| Aura Power Solar UK 2 Ltd | Bristol | 2019 |
| Aura Power Solar UK 3 Ltd | Bristol | 2019 |
| Aura Power Solar UK 4 Ltd | Bristol | 2019 |
| Aura Power Solar UK 5 Ltd | Bristol | 2019 |
| Aura Power Solar UK 6 Ltd | Northampton | 2019 |
| Aura Vayu Ltd | Bournemouth | 2025 |
| Aura Wind (Alize) Limited | Edinburgh | 2015 |
| Aura Wind (Back Lane) Limited | London | 2012 |
| Aura Wind (Badentoul) Limited | London | 2013 |
| Aura Wind (Boddington) Limited | London | 2009 |
| Aura Wind (Bridgend) Limited | London | 2013 |
| Aura Wind (Clonherb) Limited | London | 2013 |
| Aura Wind (Cowiehill) Limited | London | 2013 |
| Aura Wind (East Town) Limited | London | 2013 |
| Aura Wind (Eastertown) Limited | London | 2013 |
| Aura Wind (Erith) Limited | London | 2012 |
| Aura Wind (Hamsin) Limited | Edinburgh | 2015 |
| Aura Wind (Harrington Parks) Limited | London | 2013 |
| Aura Wind (High Dyke) Limited | London | 2014 |
| Aura Wind (Longlands Lane) Limited | London | 2014 |
| Aura Wind (LOW Bowhill) Limited | London | 2013 |
| Aura Wind (LOW Lanrigg) Limited | London | 2012 |
| Aura Wind (Martinhill East) Limited | London | 2013 |
| Aura Wind (Melbur) Limited | London | 2012 |
| Aura Wind (Merthyr) Limited | London | 2011 |
| Aura Wind (Middleton) Limited | London | 2013 |
| Aura Wind (Midtown of Glass) Limited | London | 2014 |
| Aura Wind (Newton of Edingight) Limited | London | 2014 |
| Aura Wind (North Threave) Limited | London | 2013 |
| Aura Wind (Pitcairlie) Limited | London | 2013 |
| Aura Wind (Plasparcau) Limited | London | 2014 |
| Aura Wind (Prospect House) Limited | London | 2014 |
| Aura Wind (Prustacott Farm) Limited | London | 2013 |
| Aura Wind (Samples Farm) Limited | London | 2013 |
| Aura Wind (Stonehaven) Limited | London | 2014 |
| Aura Wind (Temple Hill) Limited | London | 2015 |
| Aura Wind (Tregony) Limited | London | 2015 |
| Aura Wind (Treleigh Farm) Limited | London | 2013 |
| Aura Wind (Wairds of Alpity) Limited | London | 2014 |
| Aura Wind (Westwood Farm) Limited | London | 2013 |
| Aura Wind (Windmills NO 1) Limited | Belfast | 2012 |
| Aura Wind (Windmills NO 2) Limited | Belfast | 2012 |
| Auravive Energy Ltd | Sheffield | 2026 |
| Aurion Solar Limited | Newport Pagnell | 2025 |
| Aurora 22 Ltd | Dundee | 2026 |
| Aurora Energy Limited | Evesham | 2004 |
| Aurora Green Ltd | Glasgow | 2019 |
| Aurora Solar Farm Limited | London | 2019 |
| Aurum Solar Bodmin Limited | Birmingham | 2013 |
| Austin Broady Associates Limited | Sandbach | 2011 |
| Australis (Data) Ltd | London | 2024 |
| Autek Energy Limited | London | 2021 |
| Auto Cool Services (UK) Ltd | Halifax | 2013 |
| Autocool Air CON Limited | Bexhill On Sea | 2022 |
| Automotive Engineering Technologies UK Limited | Fareham | 2008 |
| Autonomous Investments (Developments) Ltd | Bristol | 2019 |
| Autumn 2 Summer AC Limited | Abercynon | 2017 |
| Autumnus Energy Limited | Wadebridge | 2014 |
| Avanis Energy Ltd | Denny | 2026 |