| Arbe Hypermall Limited | Wholesale & retail | 2024 |
| Arbe Loquero Limited | Construction | 2017 |
| Arborjack Limited | Agriculture & fishing | 2021 |
| Arbour Avenue Ltd | Wholesale & retail | 2025 |
| ARC (U.K.) Systems Limited | Manufacturing | 1992 |
| Arca Partners Limited | Professional & scientific | 2024 |
| Arcabi Limited | Construction | 2020 |
| Arch 8 Limited | Professional & scientific | 2008 |
| Arch Construction & Groundworks Ltd | Construction | 2008 |
| Archea Solutions Ltd | Professional & scientific | 2025 |
| Archer Trading and Consulting Limited | Information & communication | 2018 |
| Archers Field Management Company Limited | Households | 2010 |
| Arda Construct Ltd | Construction | 2024 |
| Ardi Construction Ltd | Construction | 2022 |
| Ards Group Limited | Wholesale & retail | 2020 |
| Area 3 Limited | Real estate | 2022 |
| Area Quantity Surveying Limited | Professional & scientific | 2025 |
| Arec Ltd | Wholesale & retail | 2022 |
| Argent FM Limited | Administrative & support | 1986 |
| ARGENTINA2022 Limited | Manufacturing | 2022 |
| Aria Broadband Limited | Information & communication | 2014 |
| Arikglobal Care Services Limited | Professional & scientific | 2021 |
| Arin Technologies Limited | Information & communication | 2015 |
| Ariora Ltd | Professional & scientific | 2026 |
| Ariscote Ltd | Transport & logistics | 2025 |
| Arise Abode Limited | Real estate | 2025 |
| Ariur Studio Limited | Manufacturing | 2025 |
| Arkidec Limited | Administrative & support | 2022 |
| ARM9 Services Limited | Professional & scientific | 2016 |
| Arma Falcon Motors Ltd | Wholesale & retail | 2026 |
| Armenid Ltd | Wholesale & retail | 2020 |
| Armfield Glass Limited | Professional & scientific | 2008 |
| Armfield Glass UK Limited | Construction | 2014 |
| Armonde Ltd | Hospitality | 2023 |
| Arms Security Ltd | Administrative & support | 2024 |
| ARN Services (Essex) Limited | Other services | 2019 |
| Arooj’S Beauty Lounge Ltd | Other services | 2025 |
| Around the Clock 24 Ltd | Professional & scientific | 2022 |
| ARP Flooring Limited | Construction | 2026 |
| Arro Limited | Wholesale & retail | 2025 |
| Arrymed (UK) Ltd | Wholesale & retail | 2012 |
| Arshod ALI Housing Limited | Real estate | 2022 |
| Art Brix Limited | Construction | 2025 |
| Art Rider Training Limited | Education | 2009 |
| Art-Sew-Design Limited | Manufacturing | 2009 |
| Artcraft Associates Limited | Professional & scientific | 2008 |
| Arthi Supermarket Ltd | Wholesale & retail | 2023 |
| Arthur Jack Roofing Limited | Construction | 2021 |
| Artiom Ciobanu Ltd | Wholesale & retail | 2021 |
| Arvi Properties Ltd | Real estate | 2022 |
| AS Construct Ltd | Construction | 2017 |
| AS Environmental Limited | Water & waste | 2026 |
| AS Team Advisory Limited | Information & communication | 2016 |
| Asandra Studios Ltd | Wholesale & retail | 2023 |
| Asap Clearance Limited | Construction | 2019 |
| Asap Plant Hire Ltd | Administrative & support | 2026 |
| Asap Popa Limited | Transport & logistics | 2025 |
| Ascend Rope Access Services Ltd | Construction | 2023 |
| Ascendance IT Limited | Other services | 2019 |
| Ascot Investment Management Limited | Financial services | 2002 |
| ASD Microelectronics Limited | Information & communication | 1998 |
| ASE Interactive Services Limited | Information & communication | 2009 |
| Asecondchance Ltd | Education | 2009 |
| Asglovan Limited | Construction | 2019 |
| ASH Floors Ltd | Construction | 2026 |
| ASH J Woodward Studios Ltd | Professional & scientific | 2026 |
| Ashcroft Global Ltd | Administrative & support | 2017 |
| Ashfield Court 102 AR Ltd | Households | 2020 |
| Ashgarden Investments Limited | Real estate | 2022 |
| Ashingdon Holdings Limited | Financial services | 2017 |
| Ashingdon Transport Limited | Transport & logistics | 2012 |
| Ashington Consulting Limited | Professional & scientific | 2014 |
| Ashmead Abbey Consulting Limited | Professional & scientific | 2019 |
| Ashmore Roofing Ltd | Construction | 2022 |
| Ashoka Group Limited | Financial services | 2024 |
| Ashton Property and Lettings Limited | Real estate | 2021 |
| ASI Building Restoration & Conservation Limited | Construction | 2017 |
| ASK Double Glazing Ltd | Construction | 2025 |
| ASL Builders Ltd | Construction | 2025 |
| ASL Lockers Ltd | Wholesale & retail | 2022 |
| ASL Property Management Limited | Real estate | 2023 |
| ASM Investment Group Ltd | Financial services | 2026 |
| ASM Truck Diagnostics Limited | Manufacturing | 2012 |
| ASM Truck Rentals Ltd | Administrative & support | 2019 |
| ASM Utilities Limited | Construction | 2021 |
| Asociatia Moldovenilor DIN Marea Britanie (Ammb) CIC | Education | 2026 |
| Aspar Solutions Limited | Information & communication | 2021 |
| Aspect Contracts Limited | Water & waste | 2007 |
| Aspect Drives & Patios by Design Ltd | Administrative & support | 2021 |
| Aspect Plus Limited | Administrative & support | 2014 |
| Aspect Roofing & Building by Design Ltd | Construction | 2025 |
| Aspects Carpentry & Joinery Limited | Construction | 1999 |
| Asphalt Armour Ltd | Construction | 2026 |
| Aspira Commerce Ltd | Wholesale & retail | 2025 |
| Aspiration Care Limited | Health & social care | 2012 |
| Aspire Counselling Academy Ltd | Education | 2024 |
| Aspirefootballcoaching Ltd | Arts & recreation | 2024 |
| Aspland Designs Ltd | Manufacturing | 2021 |
| ASR Forwarding Limited | Transport & logistics | 2009 |
| Assa Properties Ltd | Real estate | 2024 |