| AMP Strategic Land Limited | Real estate | 2006 |
| Ampac Europe Limited | Wholesale & retail | 1998 |
| Amplace Ltd | Wholesale & retail | 2021 |
| Amploco LLP | | 2022 |
| AMT Signature Construction Ltd | Professional & scientific | 2025 |
| AMT Signature Rental Ltd | Real estate | 2023 |
| AMW Properties Limited | Real estate | 2011 |
| AMY Nails Salon Limited | Other services | 2025 |
| Anderson & Co Publishing Limited | Information & communication | 2009 |
| Andrew M. Winch Limited | Construction | 1973 |
| Andy Racey Geoscience Limited | Professional & scientific | 2014 |
| Angel Court (Compton) Maintenance Limited | Households | 1966 |
| Angels Cleaning Alton Ltd | Administrative & support | 2023 |
| Angora Homes Ltd | Real estate | 2025 |
| Another Managed IT Services Ltd | Information & communication | 2024 |
| Anstey Road Management Company Limited | Administrative & support | 1991 |
| Ant's Home Improvements Ltd. | Construction | 2019 |
| Anthology Media Ltd | Administrative & support | 2018 |
| ANY Vehicle Hire Limited | Administrative & support | 2026 |
| Apalis Ltd | Professional & scientific | 2025 |
| Apex Media Ltd | Information & communication | 2004 |
| Apex Refrigeration & Air Conditioning Limited | Construction | 2006 |
| Apollo Beauty Ltd | Other services | 2024 |
| Apollo Creative Communications Limited | Professional & scientific | 2016 |
| Applegate Home Improvements Limited | Construction | 2003 |
| Appleton View Ltd | Real estate | 1994 |
| Appyquote Ltd | Information & communication | 2022 |
| Aqua Financial Limited | Administrative & support | 2011 |
| Aqua Tech Fleet Limited | Administrative & support | 2005 |
| Aquafine (UK) Ltd | Water & waste | 2012 |
| Aquavent Limited | Other services | 2002 |
| AR Griffin Limited | Information & communication | 2006 |
| Araldo Holdings Limited | Financial services | 2025 |
| Araldo Limited | Professional & scientific | 2008 |
| Arbaware Tree Care Ltd | Agriculture & fishing | 2022 |
| Archersway Game & Gundogs Ltd | Agriculture & fishing | 2014 |
| Archoak Aviation Ltd | Manufacturing | 2013 |
| ARG Hampshire Ltd | Hospitality | 2024 |
| Arnold Electrics Ltd | Construction | 2023 |
| Aroc Beenham Limited | Construction | 2017 |
| Aroncorp Limited | Real estate | 2000 |
| Arqi - Tech Limited | Construction | 2015 |
| Arrow Precision Engineers Limited | Other services | 2022 |
| Arrow Precision Facilities Limited | Other services | 2022 |
| Arrow Precision Manufacturing Limited | Manufacturing | 2017 |
| Artland Limited | Construction | 2004 |
| Arturion Ltd | Wholesale & retail | 2021 |
| Arvi Associates Limited | Hospitality | 2008 |
| Ascolto Limited | Professional & scientific | 1999 |
| ASH Mcmahon Creative Ltd. | Professional & scientific | 2017 |
| Ashford Cadrive Ltd | Administrative & support | 2024 |
| Ashleigh Mackay & Associates Ltd | Financial services | 2007 |
| Asmr Media Limited | Information & communication | 2026 |
| Asnk Holdings Ltd | Financial services | 2025 |
| Asnpss Limited | Financial services | 2021 |
| Asp-Inns Limited | Hospitality | 2003 |
| Aster Building Services Limited | Construction | 2004 |
| Astley-Headley Investments Ltd | Real estate | 2018 |
| Atelier Plus Architecture and Urban Design Ltd | Professional & scientific | 2023 |
| Athena 1973 Limited | Extraterritorial | 2013 |
| Atherton Cardrive Ltd | Administrative & support | 2024 |
| Athertongreenart Ltd | Wholesale & retail | 2018 |
| ATI Fire & Security Limited | Administrative & support | 2024 |
| ATI Holdings Limited | Financial services | 2020 |
| ATI Hospitality Limited | Construction | 2026 |
| Atlantic Time Tunnel Limited | Information & communication | 1991 |
| Atlas Astra Ltd | Real estate | 2026 |
| ATTACH2 Ltd | Wholesale & retail | 2023 |
| Attain Wealth Management Limited | Professional & scientific | 2010 |
| Atticus Financial Planning Ltd | Financial services | 2020 |
| Aubis Ltd | Information & communication | 2025 |
| Aubree Ltd | Construction | 2017 |
| Audio Pinnacle Limited | Wholesale & retail | 2017 |
| Augustus Oils Limited | Manufacturing | 1985 |
| Auriqa Ltd | Information & communication | 2025 |
| Austen Park (Alton) Management Co. Limited | Households | 1985 |
| Authentic Psychology Ltd | Education | 2023 |
| Auto Panel Craft Limited | Wholesale & retail | 2014 |
| Autologic Doors & Gates Ltd | Construction | 2021 |
| Autus Management Limited | Professional & scientific | 2010 |
| Auxilio Consulting Limited | Professional & scientific | 2012 |
| Avalon Garden Centre Limited | Wholesale & retail | 2009 |
| Avenida Limited | Real estate | 1999 |
| Avenue Nurseries Garden Centre Limited | Administrative & support | 2001 |
| Avid Lettings Limited | Real estate | 2023 |
| AVISON360 Limited | Professional & scientific | 2016 |
| Awakening Movie Limited | Information & communication | 2021 |
| Awesome Forecast Limited | Information & communication | 2020 |
| Awltech PFE Limited | Wholesale & retail | 2006 |
| AWR Properties Limited | Real estate | 2010 |
| Axion Testing Solutions Limited | Professional & scientific | 2025 |
| Ayodeks Ltd | Wholesale & retail | 2020 |
| B & B CR Limited | Professional & scientific | 2005 |
| B G Soutar Ltd | Administrative & support | 2014 |
| B L V H Limited | Administrative & support | 2003 |
| B20 & Capital Ltd | Professional & scientific | 2023 |
| B20 & Scull Limited | Professional & scientific | 2023 |
| B20 Limited | Professional & scientific | 2003 |
| Baby Small Boutique Ltd | Wholesale & retail | 2024 |
| Backyard Burger & Wings Ltd | Hospitality | 2020 |