| Association of Certified Commercial Diplomats | London | 2006 |
| Association of Health Reformers C.I.C. | London | 2021 |
| Assuage Healthcare Ltd | Lincoln | 2020 |
| Assure Compliance Services Ltd | Antrim | 2021 |
| Assure Fire Safety Solutions Ltd | Treorchy | 2025 |
| Assure Fire Safety Training Ltd | Stafford | 2019 |
| Assured Care Services (MK) Ltd | Milton Keynes | 2021 |
| Assured Healthcare Ltd | Chatham | 2020 |
| Assured Living Care Services Limited | Nuneaton | 2023 |
| Assured Training Support Ltd | Reading | 2024 |
| AST Global Limited | Manchester | 2009 |
| Astanamdes Ltd | Leicester | 2021 |
| Astancare Limited | Manchester | 2025 |
| Astec Consultant Services (HS) Limited | Harrow | 2014 |
| Astfire Limited | London | 2021 |
| Astm International UK | Maidstone | 2021 |
| Aston Mahoney Limited | Stratford Upon Avon | 2014 |
| Astoria Elite Care Limited | Worcester | 2022 |
| Astro Technical Services Ltd | Maidstone | 2023 |
| Astute Fire Engineering Ltd | Largs | 2017 |
| Astute Innovative Healthcare Ltd | Manchester | 2021 |
| ASW Defence Services Limited | Exmouth | 2021 |
| AT Home With Marvel Ltd | Swinscoe | 2022 |
| AT One Therapy and Wellbeing Ltd | Northampton | 2023 |
| AT Pace CIC | Birmingham | 2020 |
| AT Research and Development Ltd | Redruth | 2018 |
| ATA Carnet Express Ltd | Ashford | 2022 |
| Atazen Ltd | London | 2018 |
| Athena Business Solutions Ltd | Cleethorpes | 2025 |
| Athena Estate and Bereavement Support Limited | Coventry | 2024 |
| Athena Medical Ltd | Felsted | 2022 |
| Athletes in the Zone Foundation CIC | Birmingham | 2024 |
| Atif Warraich Limited | Hove | 2017 |
| Atimak Ltd | Bath | 2026 |
| Atiresh Limited | Hebden Bridge | 2020 |
| Atkom Limited | Manchester | 2019 |
| Atlantas Group Ltd | Harrogate | 2019 |
| Atlas Defence Group Ltd | Bath | 2026 |
| Atlas Enforcement Limited | Derby | 2006 |
| Atlas Fire Alarms Ltd | London | 2023 |
| Atlas Fire Limited | London | 2021 |
| Atlas Fire Solutions Ltd | Barrow-In-Furness | 2025 |
| Atlas Home Care Ltd | Manchester | 2022 |
| Atock Homes and Care Services Ltd | Cardiff | 2018 |
| Atoz Education Services Limited | London | 2013 |
| Atrom Mindcare Limited | London | 2023 |
| Attaintransformation Ltd | Norwich | 2025 |
| Attendance Allowance Services Ltd | London | 2024 |
| Attentive Fire Limited | London | 2015 |
| Attique 1789 Limited | Sheffield | 2020 |
| AU Pharmacare Ltd | Bury | 2023 |
| Auburn Ltd | Wallingford | 2022 |
| Audace Consulting Limited | Devizes | 2023 |
| Audiohub Ltd | Leeds | 2024 |
| Audiologycqc Limited | Sheffield | 2023 |
| Audrika and Co Limited | Maidstone | 2023 |
| Aughton Ainsworth International Foundation | Manchester | 2006 |
| Auia Ltd | Blackburn | 2022 |
| AUM F CIC | Southall | 2024 |
| Aura Health & Beauty Ayrshire Ltd | Dalry | 2025 |
| Aurea Care Limited | London | 2024 |
| Aurelia Care Ltd | Swindon | 2023 |
| Aurika Consulting Limited | Wokingham | 2025 |
| Aurora Austral Ltd | Sheffield | 2022 |
| Aurora Defence Ltd | London | 2025 |
| Aurora Healthcare Ltd | Hayes | 2023 |
| Aurum Standard Living Limited | London | 2022 |
| Auspicious Auber Ltd | Manchester | 2021 |
| Aussie Logistics Limited | Ruislip | 2014 |
| Austra Security Limited | London | 2026 |
| Australian Submarine Corporation Limited | London | 2024 |
| Autentic Care Ltd | London | 2022 |
| Auterion UK Ltd | Norwich | 2025 |
| Authentic & Care Services Ltd | London | 2019 |
| Authentic Teaching CIC | Sheffield | 2025 |
| Authorised Compliance Ltd. | Altrincham | 2024 |
| Autism and Neurodiversity Coaching Limited | Mansfield | 2023 |
| Autism Embrace for Mothers and Children CIC | Liverpool | 2024 |
| Autism Support Centre CIC | Witham | 2026 |
| Autisme Solutions Ltd | Gravesend | 2023 |
| Autofirex Limited | Stonehouse | 2018 |
| Automate-Us Ltd | Brierley Hill | 2024 |
| Auxiliary First Care Ltd | Stoke-On-Trent | 2021 |
| Auxiliumplusuk Limited | Swindon | 2018 |
| AV Fire Solutions Ltd | Bolton | 2026 |
| AVA Poppy Ltd | Waterlooville | 2026 |
| Avabelle Limited | Penarth | 2018 |
| Avah Home Care Limited | Belfast | 2023 |
| Avalon Roundhouse Collective CIC | Glastonbury | 2025 |
| Avaly Sunshine Limited | Coventry | 2023 |
| Avamei UK Ltd | Walsall | 2019 |
| Avap C.I.C. | Waterlooville | 2026 |
| AVD Fire Limited | Stoke-On-Trent | 2023 |
| AVE Fenix Limited | London | 2024 |
| Avent Healthcare Solutions Limited | London | 2022 |
| Avenue Doctors Limited | Seaham | 2017 |
| Averis Health Limited | Stockport | 2025 |
| Avey Ltd | Leeds | 2026 |
| Avi-Aura Advanced Aesthetics Academy Ltd | Sheffield | 2026 |
| Aviation Systems Consultancy Ltd | Washington | 2007 |