| Arjunli Limited | Hospitality | 2024 |
| ARK Aerospace Management Systems Limited | Transport & logistics | 2020 |
| ARK Network Solutions Limited | Professional & scientific | 2023 |
| ARK Shared Services Ltd | Information & communication | 2025 |
| Arkas Global Ltd | Wholesale & retail | 2025 |
| Arkell Land Ltd | Extraterritorial | 1914 |
| Arkell's Brewery Limited | Manufacturing | 1927 |
| Arkhomes Supported Living Ltd | Health & social care | 2021 |
| Arks Dispensary Ltd | Wholesale & retail | 2022 |
| Arlune Ltd | Wholesale & retail | 2025 |
| ARM2ARM Support Ltd | Health & social care | 2022 |
| ARN Homes Limited | Real estate | 2024 |
| Arnd Consultancy Ltd | Professional & scientific | 2017 |
| Arol Consulting Ltd | Financial services | 2011 |
| Aroma Relaxing Spa Ltd | Other services | 2025 |
| Arometa Ltd | Hospitality | 2024 |
| Arpia Group Ltd | Construction | 2022 |
| Arpia Plumbing and Heating Ltd | Construction | 2024 |
| Arpico Europe Limited | Administrative & support | 2002 |
| Array Genomics Limited | Administrative & support | 2015 |
| Arrb Services Limited | Professional & scientific | 2015 |
| Arrow HR Ltd | Administrative & support | 2016 |
| Art Industries Ltd | Professional & scientific | 2021 |
| Art Traffic Management Limited | Construction | 2017 |
| Artan Renovations Limited | Construction | 2023 |
| Artejano Limited | Other services | 1997 |
| Artejano Spa & Salon Wear Limited | Wholesale & retail | 2011 |
| Artemy Ltd | Professional & scientific | 2022 |
| Arthurian-Labs.Ai Limited | Information & communication | 2025 |
| Arthur’S Plumbing and Heating Ltd | Construction | 2019 |
| Artillery House Management Limited | Households | 2022 |
| Artimc Limited | Professional & scientific | 2013 |
| Artisan Cakes of Bath Ltd | Manufacturing | 2020 |
| Artisan Energy Limited | Professional & scientific | 2022 |
| Artizem Ltd | Professional & scientific | 2026 |
| Artsite Limited | Education | 2007 |
| Artus Limited | Professional & scientific | 2023 |
| Arual Ltd | Health & social care | 2022 |
| Arval UK Group Limited | Financial services | 1980 |
| Arval UK Leasing Services Limited | Administrative & support | 1974 |
| Arval UK Limited | Financial services | 1972 |
| Arvito Ltd | Manufacturing | 2024 |
| Arymaan Homes Limited | Real estate | 2026 |
| AS 2 Trading Ltd | Wholesale & retail | 2015 |
| AS Installs Fleet Solutions Ltd | Wholesale & retail | 2024 |
| AS Sports Ltd | Wholesale & retail | 2004 |
| AS Tasty Buns Limited | Hospitality | 2025 |
| AS Vehicle Hire Ltd | Administrative & support | 2015 |
| ASA Plumbing and Heating Ltd | Construction | 2021 |
| Asap Property Investments Ltd | Real estate | 2026 |
| Asatellus Ltd | Real estate | 2022 |
| ASC Audio Ltd | Wholesale & retail | 2023 |
| Ascend Cart Ventures Limited | Wholesale & retail | 2025 |
| Ascend Learning Trust | Education | 2011 |
| Ascend Learning Trust Enterprise Limited | Hospitality | 2010 |
| Ascend Maintenance Ltd | Construction | 2021 |
| Ascend Taekwondo LLP | | 2025 |
| Ascendo Consulting Ltd | Information & communication | 2025 |
| Ascent Leadsership Ltd | Education | 2021 |
| ASD IT Solutions Limited | Information & communication | 2025 |
| Aselsan Limited | Hospitality | 2024 |
| ASF Creative Ltd | Manufacturing | 2025 |
| ASF Signs Limited | Manufacturing | 2001 |
| ASH and Stock Limited | Real estate | 1961 |
| ASH Dredge Engineering Ltd | Professional & scientific | 2015 |
| Ash's Autos Limited | Wholesale & retail | 2013 |
| Asha Housing Ltd | Real estate | 2020 |
| Ashappuri Ltd | Wholesale & retail | 2022 |
| Ashbury Farms Contractors Limited | Agriculture & fishing | 2017 |
| Ashbury Plumbing and Heating Limited | Construction | 2017 |
| Ashcore Holdings Ltd | Wholesale & retail | 2026 |
| Ashcox Ltd | Real estate | 2014 |
| Ashdown House (Kidlington) Management Limited | Households | 2016 |
| Ashin Consultancy Limited | Information & communication | 2013 |
| Ashlar Court Swindon Residents Ltd | Households | 2001 |
| Ashlar ID Ltd | Administrative & support | 2007 |
| Ashlea Components Limited | Wholesale & retail | 1987 |
| Ashley House Specialist Dental Practice Ltd | Health & social care | 2010 |
| Ashton Barns Residents Association Limited | Households | 1997 |
| Ashton Kennedy Recruitment Limited | Real estate | 2003 |
| Ashtronix Ltd | Professional & scientific | 2019 |
| Ashwin Retail Limited | Wholesale & retail | 2025 |
| Ashworth Consulting Ltd | Professional & scientific | 2022 |
| Asian Fusion Food Ltd | Hospitality | 2025 |
| Asian Mallu Groceries Ltd | Wholesale & retail | 2024 |
| Asic Systems Ltd | Professional & scientific | 2017 |
| Asie Ltd. | Construction | 2017 |
| Asira Hair OIL Ltd | Wholesale & retail | 2021 |
| Asira Solutions Ltd | Wholesale & retail | 2023 |
| ASK Build Limited | Construction | 2016 |
| ASK Hampton Consultancy Limited | Professional & scientific | 2024 |
| ASK JO Limited | Administrative & support | 2021 |
| Askib International Limited | Wholesale & retail | 2019 |
| Askim Properties LLP | | 2025 |
| Askots Medical Services Ltd | Health & social care | 2026 |
| Aslan Electrical Services Limited | Professional & scientific | 2012 |
| Aslan Real Estate Ltd | Real estate | 2024 |
| ASM Drylining Limited | Construction | 2015 |
| Asof Developments Ltd | Construction | 2019 |
| Asof Properties Ltd | Real estate | 2024 |