| Athari Infrastructure Development Ltd | Extraterritorial | 2017 |
| Athena Dental Laboratory Limited | Information & communication | 2012 |
| Athertrend Limited | Agriculture & fishing | 1998 |
| Athlete 17 Limited | Health & social care | 2020 |
| Athletic Approach Limited | Health & social care | 2023 |
| Athletic Elite Ltd | Education | 2023 |
| Athol Ltd | Professional & scientific | 2014 |
| Athvick Retail Ltd | Wholesale & retail | 2024 |
| ATIME4CHANGE Ltd | Health & social care | 2025 |
| ATK EHS Solutions Ltd | Professional & scientific | 2024 |
| Atkins Electrical Ltd | Construction | 2012 |
| Atkinson Commercial & Domestic Services Ltd | Construction | 2026 |
| ATL Vehicle Technology Limited | Information & communication | 2007 |
| Atlantech Soft Ltd | Information & communication | 2022 |
| Atlantic Construction Services Ltd | Construction | 2023 |
| Atlantic Gateway Initiative Limited | Financial services | 2025 |
| Atlantic Inn Porthleven Ltd | Hospitality | 2024 |
| Atlas Advantage Limited | Information & communication | 2024 |
| Atlas Building (Barwell) Limited | Households | 2005 |
| Atlas Courier Resources Limited | Transport & logistics | 2016 |
| Atlas Life Limited | Financial services | 2025 |
| Atlas Property Management Ltd | Households | 2019 |
| Atlas Systems Limited | Information & communication | 2011 |
| ATLAS360 Ltd | Professional & scientific | 2017 |
| Atlax Fusion Limited | Professional & scientific | 2024 |
| Atmos Innovations Ltd | Wholesale & retail | 2019 |
| ATO Transport Ltd | Transport & logistics | 2022 |
| Atom Coffee Ltd. | Hospitality | 2018 |
| Atomic Developments Ltd | Construction | 2011 |
| Atomic Interiors Limited | Wholesale & retail | 2001 |
| Atomic Science Ltd | Education | 2013 |
| ATR Consultancy Limited | Professional & scientific | 2026 |
| Atteys Limited | Professional & scientific | 2010 |
| Attington Ltd | Transport & logistics | 2014 |
| Attproductions Ltd | Arts & recreation | 2024 |
| Attractavision Limited | Information & communication | 1998 |
| Attree Estates Limited | Professional & scientific | 1986 |
| Attyla Limited | Wholesale & retail | 2025 |
| Atua Solutions Limited | Construction | 2025 |
| ATV29 Ltd | Transport & logistics | 2026 |
| Aubrey Falls Limited | Wholesale & retail | 2012 |
| Aubrey Homes Ltd | Construction | 2023 |
| Aubrey Ventures LLP | | 2025 |
| Auburn Plumbing and Heating Ltd | Wholesale & retail | 2014 |
| Auction Marketer Ltd | Professional & scientific | 2016 |
| Audial Ltd | Information & communication | 2022 |
| Audio Works Rehearsal Studios Ltd | Arts & recreation | 2024 |
| Audise by Frem Group Ltd | Wholesale & retail | 2017 |
| Audley Asset Management Ltd | Professional & scientific | 2015 |
| Augmented Group Limited | Professional & scientific | 2003 |
| Augusta Properties (Midlands) Limited | Real estate | 2026 |
| Augustus Gloop Ltd | Information & communication | 2021 |
| Auld Associates Limited | Professional & scientific | 2010 |
| AUM Herbal Ltd | Wholesale & retail | 2026 |
| Aumec Care Services Ltd | Health & social care | 2023 |
| Aumis Deals Ltd | Wholesale & retail | 2025 |
| Aumit Limited | Professional & scientific | 2015 |
| Aunty Nk’S Foods Ltd | Wholesale & retail | 2026 |
| Aura Commercial Cleaning Services Limited | Administrative & support | 2014 |
| Aura Marketing Solutions Limited | Other services | 2023 |
| Aura Power Solar UK 6 Ltd | Energy | 2019 |
| Aura Prestige Ltd | Construction | 2025 |
| Aurachain UK Ltd | Information & communication | 2019 |
| Aurae Wellness Ltd | Health & social care | 2026 |
| Auravex Ltd | Wholesale & retail | 2026 |
| Aurenthe Ltd | Wholesale & retail | 2026 |
| Auric Eusina Ltd | Professional & scientific | 2020 |
| Aurileather Ltd | Wholesale & retail | 2026 |
| Aurora Associates Ltd | Real estate | 2025 |
| Aurora Axis Limited | Manufacturing | 2023 |
| Aurora Brands Ltd | Wholesale & retail | 2023 |
| Aurore Contracts Ltd | Construction | 2023 |
| Aurum Apex Solutions Ltd | Information & communication | 2025 |
| Austec (UK) Limited | Administrative & support | 2010 |
| Austin Alexandra Co Limited | Professional & scientific | 2025 |
| Austin Holding Group Limited | Financial services | 2025 |
| Austin Investigations Ltd. | Administrative & support | 2008 |
| Austin Plastering Ltd | Construction | 2016 |
| Austin's Letting's Ltd | Real estate | 2026 |
| Australia Luxe Collective Limited | Wholesale & retail | 2009 |
| Authentic Adverts Ltd | Professional & scientific | 2024 |
| Authentic Dining Ltd | Hospitality | 2025 |
| Authentic Films Limited | Information & communication | 2007 |
| Authenticae Ltd | Professional & scientific | 2014 |
| Authenticycle Ltd | Professional & scientific | 2018 |
| Auto - Rescue Logistics Limited | Administrative & support | 2002 |
| Auto Care & FIX Ltd | Wholesale & retail | 2025 |
| Auto Centre Northampton Ltd | Wholesale & retail | 2016 |
| Auto Classics (Northampton) Limited | Wholesale & retail | 2002 |
| Auto Elite 60 Ltd | Wholesale & retail | 2020 |
| Auto ET Ltd | Wholesale & retail | 2023 |
| Auto Jony Ltd | Wholesale & retail | 2025 |
| Auto Locksmith Northampton Ltd | Wholesale & retail | 2024 |
| Auto Mike 2025 Ltd | Wholesale & retail | 2025 |
| Auto Motive Fabrication Limited | Professional & scientific | 2005 |
| Auto Refinement Limited | Wholesale & retail | 2024 |
| Auto Refurb Northampton Limited | Wholesale & retail | 2009 |
| Auto RO Mania Ltd | Wholesale & retail | 2016 |
| Auto Shift Grabber Limited | Information & communication | 2016 |
| Auto-Vogue Automotive Ltd | Wholesale & retail | 2022 |