| Approved Movers Ltd | Other services | 2023 |
| Aptean Drink-It UK Limited | Information & communication | 2015 |
| Aptean MLM Solutions UK Limited | Information & communication | 2001 |
| Apus Projects Ltd | Professional & scientific | 2017 |
| APW UK Arcco Limited | Financial services | 2021 |
| APW UK Datadas Limited | Real estate | 2021 |
| APW UK Switch Limited | Real estate | 2021 |
| APW UK Tower Holdings Limited | Financial services | 2021 |
| APW UK WIP Limited | Real estate | 2021 |
| Aqua Drainage & Jetting Services Ltd | Water & waste | 2022 |
| Aqua Luxury Limited | Wholesale & retail | 2017 |
| Aqua Park Cardiff Limited | Arts & recreation | 2016 |
| Aqua Park Grafham Limited | Arts & recreation | 2021 |
| Aqua Park Lakeside Limited | Arts & recreation | 2019 |
| Aqua Park Rutland Limited | Arts & recreation | 2016 |
| Aqua Parks Group Limited | Arts & recreation | 2016 |
| Aqua-Bright Cleaning Ltd | Administrative & support | 2008 |
| Aquaflame GAS Services Limited | Manufacturing | 2007 |
| Aquaserve (Midlands) Limited | Construction | 2015 |
| Aquion Healthcare Ltd | Manufacturing | 2026 |
| Arabella Park (Kimblewick) Management Company Limited | Households | 2024 |
| Aramason Limited | Real estate | 2001 |
| Architectural Glass Solutions Limited | Extraterritorial | 2007 |
| Arco Decorations Limited | Construction | 2012 |
| ARK Stained Glass and Leaded Lights Limited | Manufacturing | 2009 |
| Arkcom Ltd | Information & communication | 2011 |
| Arken Watch Company Limited | Manufacturing | 2021 |
| Arms Innovations Limited | Information & communication | 2021 |
| Arms Innovations Software Limited | Information & communication | 2026 |
| Arms Innovations Technology Enterprises Limited | Administrative & support | 2026 |
| Armstrong Holdings (Staffordshire) Ltd | Real estate | 2021 |
| Arrelle Limited | Administrative & support | 2012 |
| Arriba Solutions Limited | Other services | 2026 |
| Art on Ice (UK) Limited | Arts & recreation | 2025 |
| Artbeataway Ltd | Professional & scientific | 2019 |
| Article Builds Ltd | Construction | 2022 |
| Arts & Travel Ltd | Administrative & support | 2020 |
| ARX & Arbor Group Ltd | Construction | 2026 |
| Aryan Properties (Midlands) Ltd | Hospitality | 2021 |
| Asap Property Maintenance Limited | Construction | 2026 |
| ASB Holdings Limited | Professional & scientific | 2015 |
| ASB Residential Limited | Hospitality | 2015 |
| Asbury Estate Agents Ltd | Real estate | 2025 |
| Ascendit Limited | Administrative & support | 2022 |
| Ascent Collective LLP | | 2026 |
| Ascom (UK) Ltd | Information & communication | 1958 |
| Ascotjesson Ltd | Arts & recreation | 2026 |
| Ascove Limited | Arts & recreation | 2006 |
| ASD Contracts Ltd | Construction | 2005 |
| Aset Consulting Limited | Information & communication | 2011 |
| Ashbourne Horsley Ltd | Transport & logistics | 2026 |
| Ashbrook Consultancy Limited | Professional & scientific | 2023 |
| Ashbrook Group Holdings Limited | Financial services | 2023 |
| Ashbrook Property Investments Limited | Real estate | 2023 |
| Ashby Construction Midlands Limited | Construction | 2022 |
| Ashby Eco Limited | Construction | 2023 |
| Ashby Maintenance Midlands Limited | Construction | 2022 |
| Ashby Projects Ltd | Construction | 2025 |
| Ashcroft Lane Ltd | Construction | 2026 |
| Ashcroft Metals & Alloys Limited | Real estate | 2007 |
| Ashcroft Metals Limited | Wholesale & retail | 2023 |
| Ashford Building and Plumbing Limited | Construction | 2026 |
| Ashford Lodge Amenities Limited | Hospitality | 2026 |
| Ashmoor House Limited | Real estate | 2024 |
| Ashwood Law Estate Planning Ltd | Financial services | 2019 |
| Ashworth 54 Limited | Construction | 2020 |
| Asian Product Specialists Limited | Wholesale & retail | 2013 |
| Aspen Park (Haddenham) Management Company Limited | Households | 2017 |
| Aspen Professional Services Ltd | Administrative & support | 2021 |
| Aspire Lichfield Ltd | Health & social care | 2012 |
| Aspire Lichfield Properties Ltd | Health & social care | 2014 |
| Aspire Technical Solutions Ltd | Information & communication | 2008 |
| ASPIRE2LEARN Services Ltd | Other services | 2020 |
| Asset Insights Limited | Information & communication | 2018 |
| Association for Simulated Practice in Healthcare | Education | 2013 |
| Association of Respiratory Nurses | Health & social care | 2019 |
| Astaire Bespoke Limited | Construction | 2025 |
| Astaire Management Ltd | Health & social care | 2020 |
| Aster Technology UK Limited | Wholesale & retail | 2019 |
| Asterix Electrical Services Limited | Manufacturing | 2019 |
| Astero Properties Ltd | Real estate | 2020 |
| Astro Health Ltd | Information & communication | 2024 |
| Astro Mechanical Handling Limited | Administrative & support | 2004 |
| Astro Perform Ltd | Professional & scientific | 2022 |
| Astute Education Ltd | Professional & scientific | 2013 |
| ASW Insights Limited | Professional & scientific | 2025 |
| ASX Group Limited | Construction | 2025 |
| AT Jones Ltd | Real estate | 2023 |
| AT Services Engineering Limited | Manufacturing | 2015 |
| AT Solutions Ltd | Wholesale & retail | 2026 |
| At-Us Business Finance Limited | Financial services | 2013 |
| ATA Design Limited | Professional & scientific | 2010 |
| Athlete Box Limited | Wholesale & retail | 2022 |
| Atkins Build and Construction Ltd | Construction | 2019 |
| Atkinson Group Holdings Limited | Real estate | 2019 |
| Atlas Clinical Limited | Manufacturing | 1990 |
| Atlas REC2REC and Sales Recruitment Ltd | Professional & scientific | 2020 |
| Atpf Holdings Ltd | Professional & scientific | 2023 |
| Atrium Foster Care Ltd | Health & social care | 2023 |
| Attention to Detail (Midlands) Limited | Administrative & support | 2024 |