| Asws Solutions Ltd | Information & communication | 2024 |
| AT Nine Design Ltd | Professional & scientific | 2024 |
| ATA Building Services Ltd | Construction | 2020 |
| Ataru Ltd | Professional & scientific | 2023 |
| ATC Solutions Ltd | Professional & scientific | 2019 |
| Atdem Property Management Ltd | Real estate | 2025 |
| Atea Associates Limited | Professional & scientific | 2014 |
| Atelier Artists Ltd | Professional & scientific | 2023 |
| Atelier Charnaux Ltd | Construction | 2018 |
| Atelier Noir 8 Ltd | Wholesale & retail | 2025 |
| Atelier Time Limited | Wholesale & retail | 2025 |
| ATG Domestic Repairs Ltd | Other services | 2026 |
| Atham Groups Ltd | Wholesale & retail | 2019 |
| Athena Nails Studio Limited | Other services | 2025 |
| Athena Pacific Limited | Manufacturing | 2006 |
| Athers Investments Limited | Financial services | 2019 |
| Athi Estates Limited | Real estate | 2020 |
| Athira Investments Ltd | Real estate | 2020 |
| Athos Medical Technology Limited | Professional & scientific | 2014 |
| Atkinson Accounting Services Ltd | Professional & scientific | 2025 |
| Atkinson Removals Ltd | Transport & logistics | 2019 |
| Atkinson Rental Properties Limited | Real estate | 2016 |
| Atkinson Storage & Transport Ltd | Transport & logistics | 2020 |
| Atlantic Edge Ltd | Real estate | 2019 |
| Atlantic Scientific Ltd | Wholesale & retail | 2026 |
| Atlantic Wealth Management (UK) Limited | Financial services | 2013 |
| Atlantis Resources Ltd | Wholesale & retail | 2025 |
| Atlas Arboriculture Ltd | Agriculture & fishing | 2019 |
| Atlas Surveying Limited | Professional & scientific | 2024 |
| Atlassecurityalliance Limited | Administrative & support | 2022 |
| Atme Estates Limited | Real estate | 2025 |
| Atoll Protection Limited | Other services | 2019 |
| Atomic Earth Group Ltd | Manufacturing | 2024 |
| Atonia Care Limited | Health & social care | 2023 |
| Atonia Cars Limited | Wholesale & retail | 2022 |
| Atonia Homes Limited | Real estate | 2017 |
| Atonia Marketplace Limited | Wholesale & retail | 2024 |
| ATP Aquatic Ecology Ltd | Professional & scientific | 2026 |
| ATP Heating Services Limited | Other services | 2007 |
| ATR Maintenance Limited | Construction | 2015 |
| Attain Academy Partnership | Education | 2012 |
| Attain Corporate Finance LLP | | 2025 |
| Attendance & Inclusion Consultancy Ltd | Education | 2012 |
| Attendeelink Ltd | Administrative & support | 2026 |
| AU Smile Limited | Health & social care | 2011 |
| AU Travellers Ltd | Transport & logistics | 2018 |
| Aubaine London Limited | Wholesale & retail | 2025 |
| Audio Visual Incorporated Ltd | Construction | 2014 |
| Augmenta Global Ltd | Wholesale & retail | 2018 |
| Aura Executive Travel Limited | Administrative & support | 2023 |
| Aura Recruit Ltd. | Administrative & support | 2016 |
| Aurenova Sphere Ltd | Wholesale & retail | 2026 |
| Auric Electric Ltd | Administrative & support | 2017 |
| Auriga Data Services Limited | Information & communication | 2026 |
| Auriga Models Ltd | Wholesale & retail | 2025 |
| Auro Wellness Ltd. | Wholesale & retail | 2024 |
| Aurora Capital Investements Ltd | Real estate | 2026 |
| Aurora Energy Group Limited | Wholesale & retail | 2022 |
| Aurora Security Limited | Administrative & support | 2002 |
| Aurum Property Care Ltd | Administrative & support | 2025 |
| Austin Friars 2 Limited | Real estate | 2017 |
| Austin Friars Property Limited | Real estate | 2016 |
| Authoring & Management Solutions Limited | Professional & scientific | 2014 |
| Auto Medics Essex Limited | Wholesale & retail | 2019 |
| Auto Site Limited | Construction | 2026 |
| AUTO360 Ltd | Wholesale & retail | 2012 |
| Autoart Detailing Ltd | Wholesale & retail | 2024 |
| Autohouse Holdings Limited | Professional & scientific | 1995 |
| Autohouse Investments Limited | Professional & scientific | 2013 |
| Autohouse Property Services Limited | Professional & scientific | 2009 |
| Autoid Ltd. | Wholesale & retail | 2015 |
| AUTOM8 Print Limited | Professional & scientific | 2021 |
| Automate Galaxy Ltd | Wholesale & retail | 2025 |
| AUTOMOTIV3 Developments Ltd | Wholesale & retail | 2022 |
| Automotive Mechanical Services Limited | Construction | 2012 |
| Automotive Software Solutions Limited | Other services | 2018 |
| Autonett Ltd | Wholesale & retail | 2023 |
| Autus Control Electronics Limited | Professional & scientific | 2013 |
| Auxserve Limited | Administrative & support | 2007 |
| AV Law Prep Ltd | Education | 2025 |
| Avalino Limited | Real estate | 1996 |
| Avanti Grange Friends & Family PTA Ltd | Professional & scientific | 2022 |
| AVB Link Ltd | Information & communication | 2009 |
| Avebury Road Management Ltd | Construction | 2013 |
| Avellite Ltd | Information & communication | 2024 |
| Avengers Group Ltd | Professional & scientific | 2016 |
| Avenley Law Limited | Professional & scientific | 2021 |
| Aventra Consulting Group Limited | Professional & scientific | 2025 |
| Avenue Financial Solutions Ltd | Financial services | 2019 |
| Avenue Road Flat Management Limited | Households | 2024 |
| Avertis Ltd | Professional & scientific | 2026 |
| Aviation Surplus Trading Ltd | Manufacturing | 2000 |
| Avon Assets Ltd | Real estate | 2026 |
| Avorix Retail Ltd | Wholesale & retail | 2026 |
| Avril Nanton Limited | Real estate | 2016 |
| Avsidya Services Ltd | Professional & scientific | 2007 |
| AW Medical Limited | Health & social care | 2019 |
| Awol Films Limited | Information & communication | 2002 |
| Aworan Limited | Wholesale & retail | 2026 |
| AWT Property Limited | Real estate | 2022 |