| Atseventysix Limited | Hospitality | 2021 |
| ATTACKING8BALL Ltd | Hospitality | 2026 |
| Atteam Trans Ltd | Transport & logistics | 2019 |
| Attega Group Limited | Administrative & support | 2020 |
| Atticus Healthcare Limited | Health & social care | 2022 |
| Attitude Choppers Ltd | Manufacturing | 2024 |
| Attitude Custom Cycles Ltd | Manufacturing | 2016 |
| Attune Acoustics Limited | Professional & scientific | 2017 |
| ATV Power Ltd | Administrative & support | 2021 |
| Audagio Services Ltd | Health & social care | 2012 |
| Audio Interface Ltd | Arts & recreation | 2024 |
| Audio Repli-Tech Limited | Manufacturing | 2025 |
| Audiology Practice UK Ltd | Wholesale & retail | 2025 |
| Audioscenic Limited | Manufacturing | 2017 |
| Auditcare Ltd | Professional & scientific | 2026 |
| Audley Developments Ltd | Real estate | 2023 |
| Audley Heritage 2 Limited | Real estate | 2025 |
| Audley Heritage Limited | Real estate | 2023 |
| Audsley Properties Ltd | Real estate | 2025 |
| Augmentaero Ltd | Information & communication | 2023 |
| Augmented Insights Ltd | Information & communication | 2018 |
| Augustin Consulting Ltd | Professional & scientific | 2021 |
| AUM Shree Krishna Ltd | Wholesale & retail | 2025 |
| Aunt Mary's Flowers Ltd | Wholesale & retail | 2019 |
| Auntie Ducks Ltd | Wholesale & retail | 2024 |
| Auntiepenny's Ltd | Manufacturing | 2023 |
| Aura Beauty Lounge Ltd | Other services | 2026 |
| Aura Bridge Solution Ltd | Administrative & support | 2026 |
| Aura Electrical Group Limited | Construction | 2026 |
| Aura Rides Ltd | Transport & logistics | 2025 |
| Aura Technology Group Ltd | Information & communication | 2019 |
| Aura Technology Limited | Information & communication | 2017 |
| Aura Wellness Lounge Ltd | Arts & recreation | 2025 |
| Aura Yacht Surveys LLP | | 2020 |
| Auranest London Limited | Manufacturing | 2025 |
| Aurel Transport Ltd | Transport & logistics | 2026 |
| Aurelius LAB Ltd | Information & communication | 2022 |
| Aurium Audiology Ltd | Health & social care | 2024 |
| Aurora & Atlas Ltd | Wholesale & retail | 2024 |
| Aurora-J Alliance Limited | Real estate | 2016 |
| Aurtea Limited | Manufacturing | 2025 |
| Aurum & Relics Ltd | Wholesale & retail | 2025 |
| Aurum Green Management Company Limited | Households | 2018 |
| Aurum Hortis Ltd | Construction | 2024 |
| Aurum Ventus Ltd | Professional & scientific | 2021 |
| Aussie Johns Mess - Catering Ltd | Hospitality | 2025 |
| Austin & Murray Limited | Wholesale & retail | 2023 |
| Austin Clark & Co Ltd | Professional & scientific | 2006 |
| Austin Exterior Cleaning Ltd | Administrative & support | 2024 |
| Austin Heating Ltd | Construction | 2019 |
| Austin Hughes Europe Limited | Wholesale & retail | 2001 |
| Austin Optoelectronics Limited | Professional & scientific | 2015 |
| Austol Limited | Real estate | 2002 |
| Authentic Only Limited | Wholesale & retail | 2016 |
| Authentisurv Ltd | Professional & scientific | 2022 |
| Auto Air Communications Limited | Information & communication | 2018 |
| Auto Assistance Limited | Wholesale & retail | 2002 |
| Auto Curators Limited | Wholesale & retail | 2014 |
| Auto Diagnostic Services Ltd | Wholesale & retail | 2023 |
| Auto Electrical Supplies (Southampton) Ltd | Wholesale & retail | 2003 |
| Auto Hampshire Ltd | Wholesale & retail | 2025 |
| Auto Pro Transport Ltd | Transport & logistics | 2026 |
| Auto Solutions GR Ltd | Wholesale & retail | 2013 |
| Auto Spa Hand Car Wash Ltd | Administrative & support | 2019 |
| Auto Trade Tyres Ltd | Wholesale & retail | 2006 |
| Auto Wear Custom Limited | Professional & scientific | 2026 |
| Auto Wheels Limited | Wholesale & retail | 2010 |
| Autolink (U.K.) Limited | Wholesale & retail | 1996 |
| Automate IT Consultancy Ltd | Information & communication | 2025 |
| Automated Gate and Door Services Limited | Construction | 1989 |
| Automoll Limited | Wholesale & retail | 2025 |
| Automotive Excellence Ltd | Wholesale & retail | 2013 |
| Automotive Glazing Ltd | Wholesale & retail | 2023 |
| Autonomous Robotics Limited | Manufacturing | 2013 |
| Autoplate UK Limited | Transport & logistics | 2006 |
| Autotech Motors Services Ltd | Wholesale & retail | 2022 |
| Autotechnix Southampton Limited | Wholesale & retail | 2011 |
| Autotune Garage Services Limited | Wholesale & retail | 1997 |
| Autovan Services Limited | Manufacturing | 1992 |
| Autovue Limited | Construction | 1984 |
| Autrac Ltd | Administrative & support | 2019 |
| Autumn Leaf Garden Works Ltd | Administrative & support | 2024 |
| Autumn Place (Southampton) Management Limited | Households | 1995 |
| Auxilio Advisors Limited | Professional & scientific | 2008 |
| AV Electrical & Property Solutions Limited | Construction | 2020 |
| AV Support Limited | Extraterritorial | 2024 |
| Avacado Properties Ltd | Real estate | 2022 |
| Avaeya Ltd | Information & communication | 2017 |
| Avalon Careers Ltd | Administrative & support | 2025 |
| Avalon Financial Associates Ltd | Financial services | 2009 |
| Avalon Financial Solutions Ltd | Financial services | 2018 |
| Avalon Rides Ltd | Transport & logistics | 2025 |
| Avangardent Ltd | Health & social care | 2019 |
| Avarri Ltd | Wholesale & retail | 2024 |
| Avask IT Services Ltd | Information & communication | 2019 |
| Avask Software Services Ltd | Information & communication | 2020 |
| AVC Training & Consultancy Ltd | Education | 2025 |
| Avdl Logistics Ltd | Transport & logistics | 2021 |
| Avdw Limited | Information & communication | 2016 |
| Avelar Aesthetics Ltd | Health & social care | 2023 |