| Archway Roadmaster UK Ltd | Construction | 2016 |
| Arctec Engineering Services Ltd. | Professional & scientific | 1995 |
| ARD Builders Ltd | Mining & quarrying | 2026 |
| Arete Solutions Limited | Professional & scientific | 2018 |
| ARG Pharm Ltd | Wholesale & retail | 2022 |
| Aria Art and Movement Community Interest Company | Arts & recreation | 2021 |
| Aria Bella Ltd | Hospitality | 2025 |
| Ariba Afrimart Ltd | Wholesale & retail | 2026 |
| Aries Bay Accomodation Limited | Hospitality | 2025 |
| Ariyoplus Limited | Wholesale & retail | 2023 |
| ARK 19 Ltd | Professional & scientific | 2023 |
| Arkesden Consulting Limited | Professional & scientific | 2023 |
| Arkley & Co Property Management Ltd | Real estate | 2025 |
| Arktek Group Limited | Wholesale & retail | 2015 |
| Arktek Insulation Limited | Wholesale & retail | 2017 |
| Armmchefs Limited | Hospitality | 2022 |
| Armour Holdings Limited | Financial services | 2019 |
| Armour Plastics Limited | Manufacturing | 1971 |
| Armstrong Rose Consulting Ltd | Professional & scientific | 2016 |
| Armstrong Rose Ltd | Professional & scientific | 2011 |
| Armstrong Rose Payroll Ltd | Professional & scientific | 2022 |
| Armstrong Safety and Training Services Ltd | Other services | 2024 |
| Armstrong Training Ltd | Education | 2025 |
| Armstrong Westgarth Law Ltd | Professional & scientific | 2024 |
| Armstrong's Guitars Limited | Arts & recreation | 2020 |
| Arnold Odontology Ltd | Health & social care | 2024 |
| Arqueros Consulting Limited | Professional & scientific | 2011 |
| Arriva BUS & Coach Holdings Limited | Professional & scientific | 1951 |
| Arriva Cymru Limited | Transport & logistics | 1919 |
| Arriva Finance Lease Limited | Financial services | 1972 |
| Arriva Holdco Limited | Financial services | 2023 |
| Arriva International Group Limited | Financial services | 2023 |
| Arriva Kent & Surrey Limited | Transport & logistics | 1911 |
| Arriva Kent Thameside Limited | Transport & logistics | 1986 |
| Arriva London Pension Scheme Trustee Limited | Financial services | 2019 |
| Arriva Merseyside Limited | Transport & logistics | 1986 |
| Arriva Midco Limited | Financial services | 2023 |
| Arriva Midlands Limited | Transport & logistics | 1987 |
| Arriva North West Limited | Transport & logistics | 1953 |
| Arriva Northumbria Limited | Transport & logistics | 1929 |
| Arriva Rail LO Limited | Transport & logistics | 2001 |
| Arriva South Eastern Rail Limited | Transport & logistics | 2009 |
| Arriva Trains Holdings Limited | Transport & logistics | 1995 |
| Arriva Trains Wales/Trenau Arriva Cymru Limited | Transport & logistics | 2001 |
| Arriva Transport Solutions Limited | Transport & logistics | 1966 |
| Arriva UK BUS Holdings Limited | Professional & scientific | 2001 |
| Arriva UK BUS Investments Limited | Administrative & support | 1964 |
| Arriva UK BUS Properties Limited | Construction | 1980 |
| Arrow Strength Coffee Ltd | Hospitality | 2024 |
| Arrow Strength Ltd | Arts & recreation | 2023 |
| Arrow Strength Property Ltd | Real estate | 2024 |
| Arshadss Ltd | Wholesale & retail | 2026 |
| Arshan Ltd | Wholesale & retail | 2022 |
| Arta & Tara Ltd | Hospitality | 2018 |
| Artefactual Media Ltd | Information & communication | 2004 |
| Artfinnest OLX Ltd | Manufacturing | 2025 |
| Arthur Willow Ltd | Professional & scientific | 2025 |
| Arts North Studios Ltd | Arts & recreation | 2025 |
| Artventurers Limited | Education | 2011 |
| ARV Studios Ltd | Arts & recreation | 2023 |
| Aryan Go Ltd | Hospitality | 2019 |
| Aryan’S Pizza Ltd | Hospitality | 2026 |
| ASA Lifting Services Ltd | Construction | 2018 |
| Asap Property Services Ltd | Financial services | 2024 |
| Ascension Signs North East Ltd | Manufacturing | 2022 |
| Ascent Extra Limited | Education | 2014 |
| ASH NM Limited | Wholesale & retail | 2022 |
| Ashar Hassan Associates Limited | Health & social care | 2012 |
| Ashay Holdings LLP | | 2017 |
| Ashbrooke Aesthetics Ltd | Health & social care | 2021 |
| Ashbrooke Funeral Directors Limited | Other services | 2001 |
| Ashbrooke Hall Freehold Management Limited | Households | 2018 |
| Ashbrooke Legal Services Ltd | Professional & scientific | 2026 |
| Ashbrooke Property Investments Limited | Real estate | 2014 |
| Ashbrooke Sports Club Limited | Arts & recreation | 2000 |
| Asher’S Solutions Limited | Hospitality | 2026 |
| Ashi Pizza Ltd | Hospitality | 2023 |
| Ashington Home Stores Ltd | Wholesale & retail | 2026 |
| Ashmore Consultancy Services Ltd | Information & communication | 2025 |
| Ashmore House Management Limited | Professional & scientific | 2015 |
| Ashness Estates Limited | Real estate | 2023 |
| Asiana Fusion (Sunderland) Ltd | Hospitality | 2011 |
| ASJ Construction Ltd | Construction | 2020 |
| ASL Fusion Limited | Professional & scientific | 2017 |
| ASL Systems Limited | Manufacturing | 1967 |
| Aslan an Ltd | Hospitality | 2025 |
| Aslan Golf and Sports Limited | Wholesale & retail | 2017 |
| ASM Communications Limited | Information & communication | 2017 |
| ASO Barber Kenton Ltd | Other services | 2024 |
| Aspect GAS Ltd | Professional & scientific | 2023 |
| Asphalt Pro Training Ltd | Education | 2026 |
| Aspire Global Education Ltd | Education | 2024 |
| Aspire North East Multi Academy Trust | Education | 2012 |
| Aspired Finance Limited | Financial services | 2018 |
| Asra IB Properties Ltd | Real estate | 2025 |
| Asrs Services Ltd | Financial services | 2026 |
| Asset Organisation Ltd | Financial services | 2015 |
| ASSET55 Ltd | Professional & scientific | 2012 |
| Assured Sleep Ltd | Manufacturing | 2021 |
| Aster Business Advisory Limited | Administrative & support | 2023 |