| ASR Labs Limited | Information & communication | 2025 |
| ASR Structural Engineering Ltd | Professional & scientific | 2014 |
| Assess Prosolutions Limited | Professional & scientific | 2025 |
| Assin Jakai Ltd | Wholesale & retail | 2020 |
| Assist Management Limited | Professional & scientific | 2023 |
| Assistance Ltd | Administrative & support | 2024 |
| Assm Limited | Extraterritorial | 2024 |
| Associated Futures Ltd | Professional & scientific | 2025 |
| Assure Claims Ltd | Information & communication | 2023 |
| AST Advisory Ltd | Professional & scientific | 2015 |
| Asten Associates Ltd | Professional & scientific | 2019 |
| Asterix Solutions Limited | Construction | 2025 |
| Astral Construction (Southern) Ltd | Construction | 2009 |
| Astral Informatics Limited | Information & communication | 2007 |
| Astral Security Windows Limited | Construction | 1998 |
| Astralogic Limited | Information & communication | 2024 |
| Astralshift Consulting Ltd | Information & communication | 2025 |
| Astrox Technologies Ltd | Information & communication | 2025 |
| Asttute Smarts Solutions Limited | Financial services | 2021 |
| AT Invest. Ltd | Real estate | 2021 |
| AT Line Construction Ltd | Construction | 2021 |
| At-Al Healthcare Limited | Wholesale & retail | 2025 |
| Atara Nail Bar Ltd | Other services | 2019 |
| Atfs Properties Ltd | Real estate | 2019 |
| Atharus Ltd | Financial services | 2018 |
| Atherapy Limited | Health & social care | 2002 |
| Atlantic Marine & Aviation LLP | | 2010 |
| Atlantic UK Properties Ltd | Real estate | 2018 |
| Atlas Growth Partners Ltd | Professional & scientific | 2022 |
| Atlas Mechanical Ltd | Construction | 2026 |
| Atlas WI Limited | Wholesale & retail | 2015 |
| Atlascart Ltd | Wholesale & retail | 2026 |
| Atomic Film Services Ltd | Professional & scientific | 2025 |
| Atta Rabbi Properties Ltd | Real estate | 2019 |
| Attlaw Security and Events Limited | Administrative & support | 2019 |
| Atuuta Limited | Health & social care | 2017 |
| Aubrey Stuart Consultancy Limited | Professional & scientific | 2016 |
| Audio Assassins Limited | Arts & recreation | 2017 |
| Augustus Cubed Ltd | Professional & scientific | 2011 |
| Augustus Enviro Ltd | Professional & scientific | 2013 |
| Aura House Real Estate Limited | Construction | 2021 |
| Aura Invest Ltd | Construction | 2026 |
| Aurora Advisory Ltd | Administrative & support | 2025 |
| Aurora Bride Outlet Ltd | Wholesale & retail | 2022 |
| Aurora Weddings Limited | Wholesale & retail | 2009 |
| Austin & Jenkins Ltd | Construction | 2011 |
| Austin Care Services Ltd | Health & social care | 2019 |
| Austin Elliots Limited | Construction | 2018 |
| Austin Jenkins Developments Ltd | Professional & scientific | 2012 |
| Auto Express Services Limited | Wholesale & retail | 2008 |
| Auto Sussex Ltd | Wholesale & retail | 2013 |
| Auto Test & Tyres Ltd | Wholesale & retail | 2010 |
| Auto-Fix-It Repairs Ltd | Wholesale & retail | 2025 |
| Automatic Door Security Ltd | Administrative & support | 2025 |
| Automation World Ltd | Information & communication | 2019 |
| Autonomy Controls Ltd | Information & communication | 2016 |
| Autorestore Limited | Wholesale & retail | 1989 |
| Auxilium Family Office Limited | Financial services | 2023 |
| Auziomf Ltd | Other services | 2024 |
| AV Capital One Limited | Real estate | 2017 |
| AV Fortunes Ltd | Real estate | 2020 |
| AV Maintain Limited | Construction | 2009 |
| Avail Project Management Limited | Real estate | 2023 |
| Avala Nanji Limited | Health & social care | 2025 |
| Avalon Corporate Development Limited | Professional & scientific | 2003 |
| Avanti Tech Limited | Information & communication | 2015 |
| Avantix Technologies Ltd | Administrative & support | 2022 |
| Avatech Ltd | Wholesale & retail | 2018 |
| AVB Electrical Limited | Construction | 2021 |
| Avenue Health Limited | Health & social care | 2012 |
| Avenue Manor Care Home Ltd | Real estate | 2008 |
| Avicenna Psychiatry Ltd | Real estate | 2018 |
| Avington Books Limited | Information & communication | 2019 |
| Avital Plumbing Heating GAS Services Ltd | Manufacturing | 2017 |
| Avon Meridian Global Limited | Information & communication | 2024 |
| Avondale Court (Sutton) Limited | Households | 2008 |
| Avonfield Properties Ltd | Real estate | 2025 |
| AVR88 Ltd | Health & social care | 2024 |
| Avsys Technology Solutions Limited | Information & communication | 2013 |
| Avyan & Emaya Investments Limited | Real estate | 2015 |
| AW Holdings (London) Limited | Real estate | 2025 |
| Awio Ltd | Wholesale & retail | 2019 |
| AWM Cheam Accountants Ltd | Professional & scientific | 2024 |
| AWS IT OPS Ltd | Information & communication | 2017 |
| AXE Capital Equity Limited | Real estate | 2023 |
| Axel Asset Management Ltd | Professional & scientific | 2024 |
| Axel Holdings LLP | | 2025 |
| Axial Technology Ltd | Information & communication | 2026 |
| Axiom Accountants and Consultants Limited | Professional & scientific | 2026 |
| Axiom Warehouse Improvement Ltd | Professional & scientific | 2026 |
| Axis Mechanical Services Ltd | Construction | 2011 |
| Axis Stone & Tiles Ltd | Wholesale & retail | 2025 |
| AYA Lebanese Shisha Lounge Ltd | Wholesale & retail | 2025 |
| Ayaan Consulting Limited | Professional & scientific | 2019 |
| Aygo Parking Ltd | Transport & logistics | 2022 |
| Aylin Fashion Ltd | Wholesale & retail | 2025 |
| Ayling & Finch Ltd | Construction | 2020 |
| Ayngaran Trading Ltd | Wholesale & retail | 2015 |
| Ayra Beauty Ltd | Wholesale & retail | 2021 |
| Aysha Real Estate Ltd | Real estate | 2021 |