| Alitech Precision Parts Limited | Professional & scientific | 2020 |
| ALL About Adventure Ltd | Education | 2019 |
| ALL Things Car Ltd | Information & communication | 2024 |
| Allen Groundcare Limited | Administrative & support | 2001 |
| Allison Mortgage Services Ltd | Financial services | 2023 |
| Allison Property Group Ltd | Real estate | 2025 |
| Allofts Ltd | Manufacturing | 2024 |
| Almanac Catering Limited | Hospitality | 2024 |
| ALP Analytics Ltd | Professional & scientific | 2011 |
| Alpha Tech GRP Ltd | Administrative & support | 2024 |
| Alphacruitment Ltd | Administrative & support | 2023 |
| Alphacyrus Limited | Administrative & support | 2006 |
| Amber Dental Staffing Limited | Administrative & support | 2021 |
| AMD Finance Ltd | Financial services | 2021 |
| Amelanchier Investments Limited | Financial services | 2017 |
| Amelec EOT Ltd | Financial services | 2025 |
| Amelec Technical Solutions Limited | Manufacturing | 2004 |
| Ami-Con Supplies Limited | Wholesale & retail | 2000 |
| Amita Healthcare UK Ltd | Wholesale & retail | 2019 |
| Amitha Limited | Administrative & support | 2025 |
| Amps Electrical Limited | Construction | 2004 |
| AMR Commerce Limited | Administrative & support | 2020 |
| AMR GP Holdings Limited | Financial services | 2021 |
| AMR GP Limited | Arts & recreation | 2018 |
| AMR GP Services Limited | Information & communication | 2021 |
| AMR Performance Aerodynamics Limited | Professional & scientific | 2022 |
| AMR Performance Group Limited | Financial services | 2022 |
| AMR Performance Technologies Limited | Administrative & support | 2020 |
| AMR Towcester Limited | Hospitality | 2026 |
| AMS 2608 Limited | Information & communication | 2006 |
| Ananas Digital Limited | Information & communication | 2019 |
| ANB Safety Ltd | Professional & scientific | 2012 |
| And/Or/If LLP | | 2006 |
| Andy Reid Paving Services Ltd | Construction | 2019 |
| Angel Electronics Limited | Manufacturing | 2020 |
| Angling on Line Limited | Wholesale & retail | 1999 |
| Anita Bolderson Ltd | Education | 2023 |
| Annie Noble Ltd | Professional & scientific | 2026 |
| Ansome Consultancy & Training Ltd | Professional & scientific | 2026 |
| Antoni Ventures Ltd | Other services | 2025 |
| AP Morton Tipper and Grab Hire Limited | Administrative & support | 2015 |
| Ap&I Ltd | Real estate | 2015 |
| Apercus MLR Ltd | Professional & scientific | 2026 |
| Apliko Ltd | Financial services | 2021 |
| Apollo Marketing Limited | Wholesale & retail | 2013 |
| APR Enterprises Ltd | Professional & scientific | 2021 |
| Aquatech Services Limited | Construction | 1998 |
| Aquitaine (Building Services) Limited | Construction | 2010 |
| Aquitaine Holdings Limited | Construction | 2024 |
| AR12 Productions Ltd | Arts & recreation | 2019 |
| AR12 Properties Limited | Real estate | 2024 |
| ARC Industries Limited | Professional & scientific | 2025 |
| Arcatone Limited | Information & communication | 2022 |
| Archi-Tec Architectural Design Limited | Professional & scientific | 2015 |
| Architectural Glazing Parts Limited | Wholesale & retail | 2013 |
| Arden Coffee Limited | Manufacturing | 2004 |
| Ariel Inclusive Learning CIC | Education | 2025 |
| Ariel Training and Consultancy Limited | Professional & scientific | 2022 |
| Arnott Holdings Ltd | Manufacturing | 2021 |
| Artemis Landscape Architects Ltd | Professional & scientific | 2021 |
| Artifex Build Ltd | Other services | 2020 |
| Artifex Property Ltd | Real estate | 2025 |
| Arvas Limited | Extraterritorial | 2009 |
| AS One Solutions (Bradden) LLP | | 2020 |
| AS One Solutions Ltd | Professional & scientific | 2019 |
| AS Retail Consultancy Ltd | Professional & scientific | 2021 |
| Asgard Systems Ltd | Wholesale & retail | 2025 |
| ASH Global Investments Limited | Real estate | 2025 |
| Ashburton Portman Limited | Extraterritorial | 2021 |
| Ashman & Clough Limited | Other services | 1972 |
| Ashton Cook Limited | Households | 2021 |
| Asirius Ltd | Professional & scientific | 2019 |
| Askari Blue Ltd | Information & communication | 2019 |
| Aspire Personnel Limited | Administrative & support | 2009 |
| Aspirotech Solutions Limited | Construction | 2016 |
| Asset 271 Limited | Professional & scientific | 2016 |
| Asset 272 Limited | Professional & scientific | 2016 |
| Asset 273 Limited | Professional & scientific | 2016 |
| Asset 274 Limited | Professional & scientific | 2016 |
| Asset 275 Limited | Professional & scientific | 2016 |
| Asset 276 Limited | Professional & scientific | 2016 |
| Asset 277 Limited | Professional & scientific | 2016 |
| Asset 278 Limited | Professional & scientific | 2016 |
| Asset Dynamics Group Limited | Manufacturing | 2022 |
| Associated Experts Ltd | Information & communication | 2018 |
| Assystance Limited | Administrative & support | 2011 |
| Astmoor Finance Ltd | Financial services | 2019 |
| Aston Martin Performance Technologies Limited | Professional & scientific | 2021 |
| Atg.Ce Ltd | Construction | 2019 |
| Athena Productions Ltd | Information & communication | 2021 |
| Atherden Racing Farriers Ltd | Agriculture & fishing | 2024 |
| Atkins Building Services Ltd | Construction | 2025 |
| Atkins Renovations Ltd | Construction | 2025 |
| Atlantechs Holdings Ltd | Financial services | 2015 |
| Atlantechs Limited | Manufacturing | 1990 |
| Atom Performance Technologies Limited | Professional & scientific | 2023 |
| Atrium GS Limited | Wholesale & retail | 2012 |
| Aubergine Fine Food and Wines Ltd | Wholesale & retail | 2011 |
| AUP Investments Ltd | Financial services | 2021 |
| Aurora Vitality Ltd | Health & social care | 2025 |