| ARP Property Investments Ltd | Real estate | 2018 |
| Arpegeo Ltd | Professional & scientific | 2025 |
| Arq&P Consult Ltd | Professional & scientific | 2007 |
| Arque Surveying Services Limited | Professional & scientific | 2022 |
| ARQUI9 Visualisation Ltd | Professional & scientific | 2014 |
| Arra Technical Solutions Ltd | Professional & scientific | 2025 |
| Array Display Limited | Professional & scientific | 2003 |
| Arrowhead Hire (Reading) Ltd | Construction | 2013 |
| Arrowhead Hire Limited | Construction | 1971 |
| Arrs Solutions Limited | Information & communication | 2019 |
| Arrun Ramabhadra Ltd | Health & social care | 2019 |
| Arsh Universal Limited | Wholesale & retail | 2015 |
| Art Body Soul Ltd | Arts & recreation | 2024 |
| Art Living Properties Limited | Real estate | 2024 |
| Art of Resin Ltd | Construction | 2024 |
| Art Print Productions (Maidenhead) Limited | Administrative & support | 1960 |
| Arta Discovery & Solutions Ltd | Information & communication | 2024 |
| Artcol Limited | Manufacturing | 2021 |
| Arteconi CGI Ltd | Professional & scientific | 2011 |
| Artem Project Limited | Arts & recreation | 2021 |
| Artemis Advisers Ltd | Professional & scientific | 2025 |
| Artesa Solutions Ltd | Professional & scientific | 2025 |
| Artflow Technology Limited | Manufacturing | 2026 |
| Arthlink Systems Limited | Information & communication | 2024 |
| Arthros Limited | Health & social care | 2017 |
| Arthtech Ltd | Information & communication | 2022 |
| Arthur C. Abbott Limited | Wholesale & retail | 1954 |
| Artichoke Caffe Crowthorne Limited | Hospitality | 2025 |
| Artichoke Crowthorne Limited | Hospitality | 2025 |
| Article 10 Integrated Marketing Ltd | Professional & scientific | 2008 |
| Articulate Software Limited | Professional & scientific | 2017 |
| Artifex Software Limited | Information & communication | 2014 |
| Artificial Grass & Landscaping Solutions Group Ltd | Administrative & support | 2022 |
| Artificial Ignorance Limited | Information & communication | 2025 |
| Artificial Integrity Limited | Information & communication | 2026 |
| Artiko Limited | Information & communication | 2012 |
| Artimus Enterprises Ltd | Information & communication | 2024 |
| Artisan Development Syndicate Limited | Construction | 2018 |
| Artisan Loaf Makers Ltd | Manufacturing | 2022 |
| Artisan Partners II Limited | Administrative & support | 2013 |
| Artisan Partners Limited | Administrative & support | 2009 |
| Artisan Partners UK LLP | | 2009 |
| Artise Business Management Limited | Professional & scientific | 2015 |
| Artnames Ltd | Information & communication | 2026 |
| Arts Access Ability CIC | Education | 2026 |
| Arts Boutique Limited | Arts & recreation | 2024 |
| Arts Digital Limited | Information & communication | 2020 |
| Arts Festivals Limited | Arts & recreation | 2004 |
| Arts Orchestral Limited | Arts & recreation | 2022 |
| Arttay Limited | Financial services | 2016 |
| Artur Property Investment Ltd | Real estate | 2025 |
| Arudra Solutions Ltd | Other services | 2018 |
| Arun Bognor Properties Limited | Real estate | 2018 |
| Arun Serviced Apartments Limited | Real estate | 2015 |
| Arvind Domus Limited | Real estate | 2025 |
| Arvind Pharma Limited | Professional & scientific | 2014 |
| Arvind Strategic Holdings Limited | Financial services | 2025 |
| Arvum Investments Limited | Real estate | 2026 |
| Arwin Wallace Limited | Wholesale & retail | 2025 |
| Arya Events Management Limited | Hospitality | 2021 |
| Arya Homes Limited | Real estate | 2017 |
| Aryana Express Ltd | Hospitality | 2025 |
| Aryav IT Consulting Ltd | Information & communication | 2016 |
| ARZ Logistics Limited | Transport & logistics | 2023 |
| AS Bar Limited | Hospitality | 2023 |
| AS Design and Trade Limited | Administrative & support | 2012 |
| AS Group Property Limited | Real estate | 2025 |
| AS Group Trading Limited | Real estate | 2025 |
| AS Growth Marketing Consultancy Ltd | Professional & scientific | 2026 |
| AS Homes Group Limited | Real estate | 2024 |
| AS Infotech Limited | Information & communication | 2022 |
| AS Logistic Works Ltd | Construction | 2019 |
| AS Property Company Limited | Real estate | 2022 |
| AS Shinfield Property Limited | Real estate | 2021 |
| AS Upsol Ltd | Information & communication | 2020 |
| AS4M Limited | Information & communication | 2005 |
| Asaa Investments Limited | Real estate | 2023 |
| Asaed Limited | Wholesale & retail | 2024 |
| Asamoah Limited | Information & communication | 2019 |
| Asamoah Property Limited | Real estate | 2020 |
| Asan Ltd | Extraterritorial | 2014 |
| Asanteman KUO Reading | Health & social care | 2025 |
| Asap Commercial Solutions Ltd | Professional & scientific | 2026 |
| Asap Copiers Ltd | Wholesale & retail | 2025 |
| Asap Corporate Limited | Transport & logistics | 2023 |
| Asar PVT Ltd | Professional & scientific | 2023 |
| ASC Homes Ltd | Real estate | 2025 |
| ASC Programmes Limited | Professional & scientific | 2015 |
| Ascarit Solutions UK Ltd | Information & communication | 2019 |
| Ascend Associates Limited | Professional & scientific | 2025 |
| Ascend Clinical Research Limited | Health & social care | 2024 |
| Ascend Sports Limited | Education | 2025 |
| Ascendra Systems Limited | Wholesale & retail | 2025 |
| Ascendraa Limited | Education | 2026 |
| Ascm Consulting Limited | Information & communication | 2013 |
| Ascot Business Park Management Company Limited | Real estate | 2007 |
| Ascot Lloyd Asset Management Limited | Financial services | 2020 |
| Ascot Progressive Ltd | Real estate | 2017 |
| Asctate Limited | Real estate | 2024 |
| ASD and GSD Limited | Real estate | 2022 |