| Astreya Limited | Information & communication | 2011 |
| Astwood CAD Ltd | Manufacturing | 2015 |
| Asymptote Capital Limited | Professional & scientific | 2023 |
| AT Asset Finance Ltd | Financial services | 2022 |
| AT Sixes and Sevens Ltd. | Wholesale & retail | 1998 |
| AT Your Service Group Limited | Information & communication | 2019 |
| Atap Properties Ltd | Real estate | 2025 |
| ATC183 Limited | Professional & scientific | 2022 |
| ATE Legal Ltd | Professional & scientific | 2021 |
| Atelier A&D Ltd | Professional & scientific | 2017 |
| Athena Precision Tools Limited | Professional & scientific | 2024 |
| Athithi Hospitality Ltd | Hospitality | 2026 |
| Athlete Potential Ltd | Wholesale & retail | 2022 |
| Athro Tayler Limited | Health & social care | 2015 |
| Atlantic + Limited | Professional & scientific | 2020 |
| Atlas Automation Systems Ltd | Wholesale & retail | 2023 |
| Atlas NIS Limited | Construction | 2016 |
| Atlas Van Lines International Ltd | Transport & logistics | 2015 |
| Atlus Advisory Limited | Professional & scientific | 2026 |
| Atmcuk. Ltd | Wholesale & retail | 2013 |
| ATN Builders Limited | Construction | 2024 |
| Atomic Type (UK) Limited | Wholesale & retail | 2006 |
| Atomx Ltd | Information & communication | 2017 |
| ATP Online Limited | Education | 2006 |
| ATP Tyres Ltd | Wholesale & retail | 2024 |
| Atrevida Consulting Limited | Information & communication | 2014 |
| Atreya Consulting Ltd | Information & communication | 2011 |
| Atropos Technologies Limited | Information & communication | 2015 |
| Atticus Marketing Limited | Professional & scientific | 1994 |
| Attivo Buckingham Gate Limited | Financial services | 2025 |
| Attivo Corporate Planning Limited | Financial services | 2021 |
| Attivo Financial Limited | Administrative & support | 2009 |
| Attivo Financial Planning Limited | Financial services | 2006 |
| Attivo Financial Services Limited | Financial services | 2006 |
| Attivo Group Limited | Professional & scientific | 2005 |
| Attivo Investments Holdings Limited | Financial services | 2024 |
| Attivo Investments Limited | Financial services | 2024 |
| Attivo Mortgage and Protection Limited | Financial services | 2021 |
| Attivo Partner Limited | Financial services | 2025 |
| Attivo Partnerships LLP | | 2025 |
| Attivo Private Clients Limited | Financial services | 2021 |
| Attivo Private Office Limited | Financial services | 2024 |
| Attivo UK Commercial Property Opportunities Fund Limited Partnership | | 2009 |
| Attwood Land Ltd | Financial services | 2024 |
| Attwood Project Management Limited | Construction | 2008 |
| AU Panache Ltd | Wholesale & retail | 2019 |
| Aubergine Physio Limited | Health & social care | 2022 |
| Aubrey Howard Property Services Ltd | Real estate | 2012 |
| Aubrey Mews Stow Management Limited | Households | 2019 |
| Audacity Consulting Ltd | Professional & scientific | 2024 |
| Audere Holdings Ltd | Financial services | 2023 |
| Auger Torque Europe Limited | Manufacturing | 1998 |
| Augsburger & Valvona Limited | Information & communication | 2014 |
| Auko Ltd | Information & communication | 2025 |
| Aura Bracknell Consultancy Ltd | Health & social care | 2023 |
| Aura Care Living Cirencester Ltd | Health & social care | 2017 |
| Aura Care Living Ltd | Health & social care | 2015 |
| Aura Design Collective Ltd | Professional & scientific | 2015 |
| Aura Pico 1 Limited | Financial services | 2023 |
| Aura Pico 2 Ltd | Financial services | 2023 |
| Aurem Care (Aaron House) Limited | Health & social care | 2016 |
| Aurem Care (Acqco) Limited | Health & social care | 2013 |
| Aurem Care (Alium) Limited | Health & social care | 2018 |
| Aurem Care (Bidco II) Limited | Health & social care | 2022 |
| Aurem Care (Bidco III) Limited | Health & social care | 2023 |
| Aurem Care (Bidco) Limited | Health & social care | 2021 |
| Aurem Care (Brimington) Limited | Health & social care | 2020 |
| Aurem Care (Buxton Lodge) Limited | Health & social care | 2004 |
| Aurem Care (Darlington Manor) Limited | Health & social care | 2026 |
| Aurem Care (Ella Mccambridge) Limited | Health & social care | 2026 |
| Aurem Care (Garden Lodge) Limited | Health & social care | 2026 |
| Aurem Care (Hillcrest) Limited | Health & social care | 2004 |
| Aurem Care (Kenwood) Limited | Health & social care | 2000 |
| Aurem Care (Kilburn) Limited | Health & social care | 2020 |
| Aurem Care (Lostock Lodge) Limited | Health & social care | 2001 |
| Aurem Care (Midco 2) Limited | Health & social care | 2022 |
| Aurem Care (Midco II) Limited | Health & social care | 2022 |
| Aurem Care (Midco III) Limited | Health & social care | 2023 |
| Aurem Care (Midco) Limited | Health & social care | 2021 |
| Aurem Care (OP1) Limited | Health & social care | 2021 |
| Aurem Care (South Haven Lodge) Limited | Health & social care | 2003 |
| Aurem Care (the Oaks) Limited | Health & social care | 1994 |
| Aurem Care (Westbank) Limited | Health & social care | 1987 |
| Aurem Care Group Limited | Health & social care | 2021 |
| Aurem Care Shared Services Limited | Health & social care | 2023 |
| Aurora Developments (UK) Limited | Extraterritorial | 2011 |
| Aurora Engineering (UK) Limited | Manufacturing | 2011 |
| Aurora Lamps Limited | Wholesale & retail | 1992 |
| Aurora Leisure Sales Ltd | Professional & scientific | 2026 |
| Aurora Plant UK Limited | Administrative & support | 2011 |
| Aurora Plumbing and Heating Ltd | Construction | 2021 |
| Austen Deane Ltd | Information & communication | 2022 |
| Austin and Wardle Holdings Limited | Financial services | 2023 |
| Austin Communications Ltd | Manufacturing | 2006 |
| Austin Crowhurst Ltd | Construction | 2026 |
| Austin Elliot Consultancy Ltd | Information & communication | 2019 |
| Austin Elliot Group Ltd | Financial services | 2023 |
| Austin Investments Unlimited | Financial services | 2017 |
| Austin Private Investments Ltd | Real estate | 2023 |
| Authentic Adventures Ltd | Administrative & support | 1997 |