| Ardent Care Ltd | Administrative & support | 2016 |
| Ardera-Rose PUB Company Limited | Hospitality | 2016 |
| Ardern Construction (Sheffield) Limited | Wholesale & retail | 1985 |
| Ardilla Limited | Real estate | 2003 |
| Ardivachar Communications Ltd | Professional & scientific | 2022 |
| Ardo Technician Ltd | Wholesale & retail | 2024 |
| Ardour Healthcare Services Ltd | Administrative & support | 2018 |
| Area 51 Holdings Limited | Financial services | 2023 |
| Area 51 Property Limited | Real estate | 2025 |
| Areeba Telecom Ltd | Information & communication | 2010 |
| Aren'T WE Havin' a Good Time Ltd | Professional & scientific | 2024 |
| Arena Auto Limited | Professional & scientific | 1995 |
| Arena Beauty Limited | Other services | 2018 |
| Arena Blinds Limited | Professional & scientific | 1992 |
| Arena Hair Limited | Other services | 2005 |
| Arena Residents Association Limited | Households | 2007 |
| Aresh Store Ltd | Wholesale & retail | 2025 |
| Arete Chairs Ltd | Other services | 2022 |
| Arete Merch Ltd | Wholesale & retail | 2018 |
| Arete NU Products Ltd | Other services | 2026 |
| Areton Limited | Manufacturing | 2015 |
| Arex-Electrical Ltd | Construction | 2022 |
| ARF Life and Health Ltd | Financial services | 2024 |
| Arfan Holdings Ltd | Financial services | 2024 |
| ARG Houses Ltd | Real estate | 2021 |
| ARG Retail Ltd | Wholesale & retail | 2011 |
| Argang Store Ltd | Wholesale & retail | 2023 |
| Argent Developments Limited | Real estate | 2024 |
| Argenta Capital Ltd | Real estate | 2012 |
| Argenta Property Ltd | Real estate | 2006 |
| Arggen 1 Limited | Health & social care | 2000 |
| Argyle Acquisitions Ltd | Financial services | 2026 |
| Argyle Property Associates Ltd | Real estate | 2022 |
| Arhan Culinary Ltd | Hospitality | 2026 |
| ARI Car Wash Ltd | Administrative & support | 2024 |
| ARI5 Logistics Ltd | Transport & logistics | 2024 |
| Aria Bidco Limited | Financial services | 2023 |
| Aria Botanica Limited | Agriculture & fishing | 2025 |
| Aria Court (Management) Limited | Households | 2003 |
| Aria Court (Sherwood) Limited | Real estate | 2015 |
| Aria Letting Limited | Real estate | 2016 |
| Aria Property Development Limited | Real estate | 2004 |
| Aria Shahrokhshahi Ltd | Professional & scientific | 2021 |
| Aria Sustainability Ltd | Professional & scientific | 2020 |
| Ariadne UK Services Ltd | Other services | 2022 |
| Ariana Supermarket Limited | Wholesale & retail | 2019 |
| Aribs Notts Limited | Hospitality | 2021 |
| Ariel Component Parts Limited | Manufacturing | 2020 |
| Ariel Motors Limited | Other services | 1993 |
| Ariel Owners Club 2020 Limited | Other services | 2020 |
| Arifs Properties Limited | Real estate | 2025 |
| Arimasec Limited | Administrative & support | 2018 |
| Ariocell Ltd | Professional & scientific | 2017 |
| Arisaig Limited | Real estate | 2002 |
| Arise and Care Limited | Health & social care | 2024 |
| Arish Theo Ltd | Real estate | 2024 |
| Aristide Ltd | Health & social care | 2022 |
| Ariva Garage Ltd | Wholesale & retail | 2020 |
| Arix IP Limited | Professional & scientific | 2022 |
| ARJ Events Ltd | Hospitality | 2023 |
| ARJ Surveying Services Ltd | Professional & scientific | 2018 |
| ARK 28 Properties Ltd | Real estate | 2023 |
| ARK Boiler Installations Ltd | Construction | 2024 |
| ARK Electric Ltd | Manufacturing | 2025 |
| ARK Feris Limited | Manufacturing | 2024 |
| ARK Fiscal Solutions Limited | Financial services | 2010 |
| ARK Property & Building Solutions Ltd | Construction | 2025 |
| ARK Transport Ltd | Transport & logistics | 2013 |
| ARK UK Bidco Limited | Financial services | 2025 |
| ARK UK Midco Limited | Financial services | 2025 |
| ARK UK Topco Limited | Financial services | 2025 |
| Arkadiusz Maciej Kulesza Ltd | Extraterritorial | 2024 |
| Arkafus Limited | Information & communication | 2024 |
| Arkenstone Engineering Ltd | Professional & scientific | 2024 |
| Arknowledge Limited | Extraterritorial | 2015 |
| Arkord Properties Ltd | Real estate | 2023 |
| Arks Projects Ltd | Financial services | 2000 |
| Arksafe Ltd | Professional & scientific | 2026 |
| Arktika (UK) Limited | Information & communication | 2005 |
| Arkwright Accountants & Tax Advisors Ltd | Professional & scientific | 2024 |
| Arkwright DRY Cleaners Limited | Other services | 2011 |
| Arkwright Investments Limited | Professional & scientific | 1985 |
| Arkwright Meadows Community Gardens | Education | 2003 |
| Arkwright Properties Limited | Professional & scientific | 1981 |
| Arkwright Property Co. Ltd | Construction | 2018 |
| Arlco Living Ltd | Real estate | 2024 |
| Arleverholdings Ltd | Hospitality | 2025 |
| ARM Catering Equipment Ltd | Wholesale & retail | 2025 |
| ARM Management Services Limited | Construction | 2022 |
| Armaan Brother Ltd | Construction | 2024 |
| Armadillo Construction Services Ltd | Wholesale & retail | 2006 |
| Armadio Store Limited | Wholesale & retail | 2023 |
| Armalloy Limited | Manufacturing | 1982 |
| Armamil Ltd | Wholesale & retail | 2024 |
| Arman Consulting Ltd | Information & communication | 2024 |
| Arman Majidi Medical Practice Limited | Health & social care | 2016 |
| Armfield Control Systems Limited | Manufacturing | 2003 |
| Armfield Haugen Enterprise Ltd | Wholesale & retail | 2021 |
| Armis Properties Ltd | Real estate | 2025 |
| Armitage Brothers Limited | Manufacturing | 1897 |