| API Robotics Engineering Limited | Professional & scientific | 2025 |
| Apiary Ltd | Agriculture & fishing | 2025 |
| APL Plastics Limited | Manufacturing | 1962 |
| Apogee Solutions Limited | Information & communication | 2011 |
| Apollo Wellness & Performance Limited | Arts & recreation | 2023 |
| Apple 2 Ltd | Other services | 2024 |
| Apple Nails BSK Ltd | Other services | 2026 |
| Apple Nails Limited | Other services | 2025 |
| Applied Production Solutions Ltd | Wholesale & retail | 2014 |
| Applied Research and Evaluation Ltd | Professional & scientific | 2024 |
| Apps in the Sky Ltd | Information & communication | 2014 |
| Aps-Technologies Ltd | Information & communication | 2023 |
| Apssent ITS Ltd | Information & communication | 2014 |
| APT Decorating Services Limited | Construction | 2021 |
| Aquabecco Ltd | Construction | 2022 |
| Aquafactors Ltd | Manufacturing | 2012 |
| Aquanet International Limited | Professional & scientific | 1992 |
| Aquarius Plumbing and Heating Services Ltd | Construction | 2025 |
| Aquarius Wireless Solutions Limited | Manufacturing | 2026 |
| Aquatec Group Limited | Manufacturing | 1990 |
| Aquatec Subsea Limited | Manufacturing | 1999 |
| Aquatec Telemetry Limited | Manufacturing | 1998 |
| Aquila IT Services Ltd | Information & communication | 2014 |
| Aquila WJS Ltd | Information & communication | 2013 |
| Aquilant Endoscopy Limited | Wholesale & retail | 1997 |
| Aquilant Limited | Wholesale & retail | 1987 |
| ARA Theoria Ltd | Wholesale & retail | 2018 |
| Araliya Professional Cleaning Limited | Administrative & support | 2014 |
| Aratus Software Limited | Information & communication | 2015 |
| Arav Consultancy Services Limited | Professional & scientific | 2022 |
| ARB One Ltd | Professional & scientific | 2007 |
| ARB Three Ltd | Professional & scientific | 2007 |
| Arbetskraft Ltd | Transport & logistics | 2011 |
| Arbor and Willow Limited | Wholesale & retail | 2018 |
| Arcanavision Limited | Information & communication | 2011 |
| Arch Clothing Company Ltd | Wholesale & retail | 2021 |
| Architectural Survey Consultants Limited | Professional & scientific | 2024 |
| Architectural Survey Services Ltd | Professional & scientific | 2016 |
| Arcible Limited | Information & communication | 2016 |
| Arcwise Consulting Limited | Information & communication | 2025 |
| Arcyro Ltd | Administrative & support | 2017 |
| Area 11 Limited | Professional & scientific | 2019 |
| Area 22 Ltd | Administrative & support | 2025 |
| Area 51 Ltd | Arts & recreation | 2017 |
| Aremo Limited | Professional & scientific | 2023 |
| ARG Automotive Limited | Wholesale & retail | 2005 |
| Argent FOX Limited | Professional & scientific | 2023 |
| Argo Creative Limited | Professional & scientific | 2010 |
| Aries UF Consultants Limited | Information & communication | 2011 |
| Arimar Logistics Ltd | Transport & logistics | 2026 |
| Arjoni Ltd | Transport & logistics | 2025 |
| Arjun Software Limited | Information & communication | 2019 |
| ARK Cancer Charity | Health & social care | 2012 |
| ARK Computer Consultancy Ltd | Information & communication | 1998 |
| ARK of Gods Covenant Outreach Ministry International | Other services | 2017 |
| ARK Tech Solutions Ltd | Information & communication | 2016 |
| Arkonia Holdings Limited | Professional & scientific | 2003 |
| ARL Properties Ltd | Real estate | 2018 |
| Arlander Limited | Transport & logistics | 2012 |
| Armadillo & Co UK Ltd | Wholesale & retail | 2020 |
| Armano Services Ltd | Wholesale & retail | 2026 |
| Armeva Limited | Real estate | 2024 |
| Armstrong Bell Properties Ltd | Real estate | 2019 |
| Armur Technologies Ltd | Information & communication | 2015 |
| Arnarge Solutions Limited | Professional & scientific | 2010 |
| Aroma Biryani Limited | Hospitality | 2025 |
| Around the K Ltd | Hospitality | 2022 |
| Aroy Thai Kitchen Ltd | Hospitality | 2025 |
| Arran Bowbanks Press Services Limited | Manufacturing | 2013 |
| Arrandahl Trading Company Ltd | Financial services | 2026 |
| Arrodale Ltd | Professional & scientific | 2026 |
| Arrow Precision Ltd | Construction | 2025 |
| Art Lover VIP Limited | Professional & scientific | 2009 |
| Arteka Limited | Professional & scientific | 2003 |
| Artisnal Bakery Ltd | Manufacturing | 2022 |
| Artmar Limited | Transport & logistics | 2021 |
| ARW Scaffolding Ltd | Construction | 2013 |
| Arztraverse Limited | Professional & scientific | 2015 |
| AS Event Mgmt Ltd | Arts & recreation | 2025 |
| Asben Services Ltd | Health & social care | 2015 |
| ASC Express Ltd | Construction | 2018 |
| Ascend Fire and Security Ltd | Administrative & support | 2020 |
| Ascendant Technology Holdings UK Limited | Professional & scientific | 2000 |
| Ascendpropertyinvestments Ltd | Real estate | 2025 |
| Ascertain Limited | Administrative & support | 2003 |
| Ascp Group Ltd | Professional & scientific | 2013 |
| ASD Drive Ltd | Construction | 2023 |
| Asdebi Enterprise Limited | Health & social care | 2023 |
| ASF Properties Limited | Real estate | 2013 |
| Asfour Crystal Limited | Extraterritorial | 2010 |
| Asgard Consulting Ltd | Professional & scientific | 2003 |
| Ash-Gb Consultancy Limited | Health & social care | 2015 |
| Asha Lalit & Co Ltd | Professional & scientific | 2008 |
| Ashby & Austin Property Services Limited | Real estate | 2006 |
| Ashby Signs Limited | Manufacturing | 1990 |
| Ashby Trade Sign Supplies Limited | Manufacturing | 1979 |
| Ashe Buchanan Associates Limited | Financial services | 2024 |
| Ashe Project Management Limited | Construction | 2021 |
| Ashe Sailing Ltd | Arts & recreation | 2015 |
| Asherandmaddoxproperties Limited | Real estate | 2024 |