| Atimak Ltd | Public administration | 2026 |
| Atis Holdings Limited | Financial services | 2025 |
| Atlantic Road Holdings Limited | Financial services | 2025 |
| Atlantic Road Properties Limited | Real estate | 2025 |
| Atlas Defence Group Ltd | Public administration | 2026 |
| Atlas Interiors Limited | Wholesale & retail | 2009 |
| Atlas Ride Ltd | Administrative & support | 2025 |
| Atoans Limited | Health & social care | 2016 |
| Atomic Lettings Ltd | Real estate | 2024 |
| Attah Medical Ltd | Health & social care | 2015 |
| Attention 2 Detail - Creative Marketing & Print Solutions Limited | Manufacturing | 2001 |
| Attewell Court Limited | Households | 1980 |
| Attika Workspace Limited | Professional & scientific | 2003 |
| Attinger Jack Holdings Limited | Financial services | 2011 |
| Attinger Jack Limited | Professional & scientific | 2010 |
| Attuned Designs Ltd | Information & communication | 2015 |
| Atum Stone Ltd | Manufacturing | 2020 |
| Auburn Music Limited | Information & communication | 2011 |
| Auctus Capital Limited | Real estate | 2004 |
| Audacious Commerce Ltd | Professional & scientific | 2026 |
| Audacious Growth Partners Ltd | Professional & scientific | 2026 |
| Audaz Global Limited | Real estate | 2023 |
| Audiburn Stables Limited | Hospitality | 2025 |
| Audience Limited | Wholesale & retail | 2000 |
| Augmind Ltd | Professional & scientific | 2016 |
| AUK Investments Group Ltd | Financial services | 2024 |
| AUK Media Ltd | Wholesale & retail | 2019 |
| AUK Property Ltd | Real estate | 2011 |
| Aumery Gardens (High Littleton) Management Company Limited | Households | 2008 |
| Aunty Marg Limited | Hospitality | 2013 |
| Aureity Technical Ltd | Information & communication | 2024 |
| Aurelius Properties Ltd | Real estate | 2024 |
| Aurimas Pukas Ltd | Health & social care | 2021 |
| Aurora Capital and Investment Ltd | Administrative & support | 2011 |
| Aurora Corporate Services Ltd | Professional & scientific | 2019 |
| Aurora Tourism Investments Ltd | Administrative & support | 1995 |
| Austin Consultants Limited | Information & communication | 2007 |
| Authentic Street Food Ltd | Wholesale & retail | 2025 |
| Autism Alphabet Limited | Health & social care | 2021 |
| Autistic EYE Community Interest Company | Wholesale & retail | 2013 |
| Auto Cellular Installations Limited | Information & communication | 2003 |
| Autoadmin Limited | Information & communication | 2025 |
| Autocheck Limited | Manufacturing | 1993 |
| Automotive Parts Distribution Group Limited | Professional & scientific | 1996 |
| Autonomous Consulting Intelligence Ltd | Information & communication | 2025 |
| Autotech (Melksham) Limited | Wholesale & retail | 2011 |
| Auxilium Administration UK Limited | Extraterritorial | 2020 |
| Auxilium Directors UK Limited | Extraterritorial | 2020 |
| Avalon Electronics Holdings Limited | Financial services | 2018 |
| Avalon Electronics Limited | Manufacturing | 1998 |
| Avalon Risk Solutions Limited | Professional & scientific | 2017 |
| Avalon Solar Technologies Ltd | Professional & scientific | 2023 |
| Avanti Surfacing Ltd | Construction | 2025 |
| Avari Technology Ltd | Information & communication | 2024 |
| AVC (Bath) Limited | Wholesale & retail | 2003 |
| Avenida Isabel Ltd | Wholesale & retail | 2011 |
| Avenir Early Years Group Limited | Financial services | 2024 |
| Avenue Country Homes Limited | Hospitality | 1959 |
| Avenue Court Development Limited | Real estate | 2016 |
| Avenue Court One Limited | Real estate | 2021 |
| Avenue Court Two Limited | Real estate | 2021 |
| Avery ROW Ltd | Wholesale & retail | 2014 |
| Aviaire Limited | Professional & scientific | 2016 |
| Avila Ltd | Professional & scientific | 2012 |
| Avolv Consulting Ltd | Information & communication | 2021 |
| Avon Cleaning Services Ltd | Administrative & support | 2026 |
| Avon Cruising Limited | Transport & logistics | 2006 |
| Avon Film Productions (Bath) Limited | Professional & scientific | 1977 |
| Avon Steel Company Limited | Wholesale & retail | 1977 |
| Avon Valley Medical Limited | Health & social care | 2013 |
| Avondale Court (Bath) Management Company Limited | Administrative & support | 2001 |
| Avondale Facilities Limited | Households | 2007 |
| Avonetix Ltd | Information & communication | 2023 |
| Avonvale Carpets Limited | Wholesale & retail | 2012 |
| AVT (UK) Limited | Wholesale & retail | 1998 |
| Avtam Limited | Professional & scientific | 2014 |
| Avygnon Limited | Financial services | 2022 |
| AW Safety Engineering Limited | Professional & scientific | 2016 |
| Awan Consultancy Limited | Health & social care | 2024 |
| Awareness and Change Ltd | Education | 2021 |
| AWP Electrical & SON Ltd | Construction | 2016 |
| Awrl Limited | Real estate | 2016 |
| AXD Engineering Group Limited | Professional & scientific | 2021 |
| AXE Medical Ltd | Health & social care | 2018 |
| Axicorda Ltd | Information & communication | 2005 |
| Axiom Special Effects Ltd | Information & communication | 2023 |
| Axis Dorset Ltd | Administrative & support | 2016 |
| Axis Events Limited | Other services | 2015 |
| Axis Fire and Security Services Limited | Construction | 1996 |
| Axis Fire Sprinklers Ltd | Extraterritorial | 2023 |
| Axis Projects Ltd | Professional & scientific | 2015 |
| Azalea Beauty Academy Limited | Professional & scientific | 2021 |
| Azate Ltd | Education | 2025 |
| Azura Stratford Limited | Construction | 2020 |
| Azure & Green Environmental Limited | Water & waste | 2018 |
| Azure Luxury Hotel Collection Limited | Administrative & support | 2001 |
| Azuze Consultancy Ltd | Professional & scientific | 2023 |
| B & D Heal Limited | Transport & logistics | 2006 |
| B & E Hastings Ltd | Health & social care | 2023 |
| B & R Thorner Limited | Construction | 1978 |