| Arjo Recruitment Limited | Real estate | 2001 |
| ARK Bristol Properties Ltd | Real estate | 2026 |
| ARK Building Contractors Limited | Construction | 2004 |
| ARK Consultancy & Training Limited | Professional & scientific | 2024 |
| ARK Ecology Ltd | Professional & scientific | 2021 |
| ARK House Vets Limited | Extraterritorial | 2010 |
| ARK Invest International Ltd | Information & communication | 2019 |
| ARK Invest UK Marketing Ltd | Information & communication | 2025 |
| ARK Property (Southwest) Limited | Real estate | 2022 |
| ARK Property Organisation Ltd | Real estate | 2024 |
| ARK Veterinary Centre (Colchester) Limited | Extraterritorial | 2014 |
| ARK Visionary Limited | Hospitality | 2021 |
| ARK Wardrobes Ltd | Construction | 2024 |
| Arka Estates Ltd | Real estate | 2022 |
| Arkade Food Ltd | Hospitality | 2023 |
| Arkadiko Partners Ltd | Professional & scientific | 2019 |
| Arkbridge Trading Limited | Manufacturing | 2026 |
| Arkhi Careers Limited | Administrative & support | 2022 |
| Arko Tharkor Group Ltd | Construction | 2020 |
| Arkta Group Ltd | Construction | 2023 |
| Arkwright Asset Management Limited | Professional & scientific | 2011 |
| ARL Appliance Repair Ltd | Manufacturing | 2024 |
| Arlalite Ltd | Real estate | 2024 |
| Arley Garage (Zetland RD) Ltd | Administrative & support | 2004 |
| Arlington Landscapes Limited | Administrative & support | 2023 |
| Arlington ROW Wealth Management Ltd | Financial services | 2024 |
| Arlington Ster Limited Partnership | | 2003 |
| Arlo Golf Co Limited | Wholesale & retail | 2024 |
| Arlo James Ltd | Wholesale & retail | 2018 |
| Arlo Pet Limited | Manufacturing | 2024 |
| ARM Housing Limited | Real estate | 2023 |
| Armada (Bristol) Limited | Construction | 2006 |
| Armada Estates Limited | Real estate | 2002 |
| Armadeli Ltd | Wholesale & retail | 2018 |
| Armadillo Associates Holdings Limited | Financial services | 2017 |
| Armadillo Associates Limited | Other services | 1992 |
| Armand Taylor and Company Limited | Manufacturing | 1932 |
| Armand&Rahela Limited | Construction | 2025 |
| Armando Trading Ltd | Wholesale & retail | 2025 |
| Armasec Security Ltd | Administrative & support | 2007 |
| Armasec Services Ltd | Administrative & support | 2024 |
| Armdaleenterprise Ltd | Wholesale & retail | 2025 |
| Armour Analytical Services Limited | Professional & scientific | 2016 |
| Armour Construction Services Limited | Construction | 2019 |
| Armourguard Engineering Limited | | 1981 |
| Armpj Ltd | Professional & scientific | 2023 |
| Armr Training Academy Ltd | Education | 2024 |
| Armstrong Holland Consultants Limited | Information & communication | 2018 |
| Armstrong Limited | Construction | 1997 |
| Armstrong Walker Holdings Limited | Other services | 2018 |
| Armstrong Way Business Park Management Company Limited | Real estate | 2020 |
| Army of Emus Ltd | Arts & recreation | 2025 |
| Arnex LP | | 2012 |
| Arno GB Limited | Manufacturing | 1978 |
| Arnold RD Property Ltd | Real estate | 2023 |
| Arnolds Way Business Park Management Company Limited | Households | 2020 |
| Arnolfini Trading Limited | Wholesale & retail | 1987 |
| Arnos Manor Hotel Limited | Hospitality | 2016 |
| Arnos Vale Cemetery Enterprises Limited | Wholesale & retail | 2010 |
| Arnos Vale Cemetery Trust | Administrative & support | 2007 |
| Arnos Vale Estates Limited | Real estate | 2022 |
| Arnos Vale Montessori Childcare Ltd | Health & social care | 2020 |
| Arnott Energy Limited | Professional & scientific | 2021 |
| ARO Business Consulting Ltd | Professional & scientific | 2011 |
| ARO Labs Ltd | Manufacturing | 2025 |
| Arobase Creative Limited | Professional & scientific | 2016 |
| Arodacia Ltd | Transport & logistics | 2019 |
| Arohanui Ventures Ltd | Education | 2020 |
| Aromyal Ltd | Wholesale & retail | 2025 |
| Arona Foods Ltd | Hospitality | 2019 |
| Around the World Trading, Ltd | Transport & logistics | 2012 |
| Arovia Global Travel Ltd | Administrative & support | 2026 |
| Arow Homes Ltd | Real estate | 2021 |
| ARR Lettings Limited | Real estate | 2018 |
| Arrai Beauty Ltd | Other services | 2025 |
| Arrakis Technologies Limited | Information & communication | 2025 |
| Arran Intelligence Ltd | Information & communication | 2026 |
| Arrancar Limited | Professional & scientific | 2002 |
| Arranet Ltd | Information & communication | 2013 |
| Arrested Company Limited | Professional & scientific | 2017 |
| Arris Homes Limited | Real estate | 2019 |
| Arron Property Ltd | Real estate | 2012 |
| Arrow Carpentry and Build Limited | Construction | 2025 |
| Arrow JIE (UK) Ltd | Hospitality | 2013 |
| Arrowline Cars Limited | Transport & logistics | 2025 |
| Arrsse (UK) Limited | Wholesale & retail | 2026 |
| ARS Artium Group Limited | Construction | 2025 |
| ARS Convenience Ltd | Wholesale & retail | 2025 |
| ARS Investments Ltd. | Real estate | 1985 |
| ARS Tech House Ltd | Information & communication | 2025 |
| Arsal Ltd Ltd | Wholesale & retail | 2022 |
| Arsb Properties Limited | Real estate | 2023 |
| Arscott Industries Limited | Wholesale & retail | 2019 |
| Arsl Hub Ltd | Wholesale & retail | 2025 |
| Art Beats Collective C.I.C. | Information & communication | 2024 |
| Art Business Ltd | Arts & recreation | 2023 |
| Art Continuum Ltd | Wholesale & retail | 2025 |
| Art Damage Limited | Wholesale & retail | 2009 |
| Art IS Hard Records Limited | Information & communication | 2012 |
| Art LAB Bristol Limited | Arts & recreation | 2023 |