| Appliance Book Ltd | Manufacturing | 2013 |
| Applied AGI Limited | Professional & scientific | 2019 |
| Applied Analytics Ltd | Professional & scientific | 2012 |
| Applied Controls UK Ltd | Professional & scientific | 2011 |
| Applied Link Bspm Ltd | Extraterritorial | 2018 |
| Applied Measurements (Holdings) Limited | Financial services | 2011 |
| Applied Measurements Limited | Wholesale & retail | 1991 |
| Applied Rfid Limited | Administrative & support | 2023 |
| Applied Traffic Limited | Manufacturing | 2001 |
| Applied VWS Limited | Manufacturing | 2025 |
| Applied Weighing International Limited | Manufacturing | 1993 |
| Appricot Limited | Information & communication | 2026 |
| Appriver UK Limited | Information & communication | 2018 |
| Apptorack Limited | Information & communication | 2020 |
| Appzen UK Ltd | Information & communication | 2018 |
| Apricot Studios Limited | Construction | 1997 |
| Aprikam Ltd | Professional & scientific | 2006 |
| Aprios Audio Visual Limited | Wholesale & retail | 2003 |
| Aprios Ltd | Extraterritorial | 2007 |
| Aprés Angels Ltd | Wholesale & retail | 2025 |
| APS Tech Consulting Limited | Information & communication | 2017 |
| Apsa Property Investments Ltd | Real estate | 2024 |
| Apsley Controls Limited | Manufacturing | 1983 |
| Aptiv Solutions (UK) Ltd | Professional & scientific | 1999 |
| Aptrac Consulting Ltd | Professional & scientific | 2024 |
| Apus Ecology Ltd | Professional & scientific | 2022 |
| APW Consultants Ltd | Construction | 2017 |
| AQ Broadcast Limited | Information & communication | 2013 |
| AQ Properties (Reading) Ltd | Real estate | 2021 |
| AQ Smile Limited | Health & social care | 2011 |
| AQS Midco Limited | Financial services | 2021 |
| AQS Operations Limited | Hospitality | 2021 |
| AQS Pbsa Holding (UK) Limited | Financial services | 2021 |
| AQS Student Property Limited | Real estate | 2021 |
| AQS Topco Limited | Financial services | 2021 |
| Aqsh Dent Limited | Health & social care | 2026 |
| Aqua Invest Limited | Real estate | 2011 |
| Aqua Vitae Sailing Limited | Administrative & support | 2006 |
| Aquacraft Ltd | Construction | 2019 |
| Aquafax Limited | Wholesale & retail | 1982 |
| Aquaflame Heating Limited | Construction | 2020 |
| Aquaforno Ltd | Wholesale & retail | 2011 |
| Aquakindly Swimming Ltd | Education | 2022 |
| Aquamatic Products Limited | Wholesale & retail | 1995 |
| Aquaphocus Limited | Professional & scientific | 2016 |
| Aquaphor UK Ltd | Wholesale & retail | 2019 |
| Aquarity Ltd | Water & waste | 2026 |
| Aquasync UK Ltd | Administrative & support | 2026 |
| Aquestex Limited | Administrative & support | 2005 |
| Aquila Air Traffic Management Services Limited | Transport & logistics | 2014 |
| AR and MS Companies Limited | Real estate | 2025 |
| AR Broadcast Services Limited | Information & communication | 2025 |
| AR GRP Limited | Real estate | 2009 |
| AR Phones & Repairs Ltd | Wholesale & retail | 2023 |
| AR Professional Limited | Professional & scientific | 2024 |
| AR Special Cleaning Ltd | Administrative & support | 2024 |
| AR360 Group Ltd | Professional & scientific | 2023 |
| ARA Catering (Reading) Ltd | Hospitality | 2022 |
| ARA Coaching Ltd | Arts & recreation | 2017 |
| ARA Properties Limited | Real estate | 2024 |
| Arabian Drive (M.C.) Limited | Households | 2022 |
| Arajagopalan Limited | Information & communication | 2025 |
| Arana UK Limited | Hospitality | 2005 |
| Aranz Medical (UK) Limited | Information & communication | 2017 |
| Arar Estates Ltd | Real estate | 2024 |
| Arasaki Ltd | Information & communication | 2022 |
| Arasta Retail Ltd | Wholesale & retail | 2026 |
| Arav IT Consultancy Limited | Information & communication | 2015 |
| Aravind Sampath Ltd | Health & social care | 2015 |
| ARB Property Solutions Ltd | Real estate | 2019 |
| Arbalest Ltd | Wholesale & retail | 2025 |
| Arborfield Court Management Company Limited | Households | 1996 |
| Arborfield Grange Management Company Limited | Real estate | 1987 |
| Arborfield Green Community Interest Company | Hospitality | 2016 |
| Arborfield Logs Supplies Ltd | Wholesale & retail | 2025 |
| Arborfield Residents (Plots 60 - 70) Management Company Limited | Households | 2020 |
| Arborfield Tree Care Limited | Administrative & support | 2016 |
| Arborheath Limited | Professional & scientific | 2020 |
| ARC BIO Communications Limited | Professional & scientific | 2016 |
| ARC Statistical Services Ltd | Professional & scientific | 2016 |
| Arca Homes Limited | Real estate | 2024 |
| Arca Origins CIC | Education | 2026 |
| Arcadia LJJ Limited | Administrative & support | 2022 |
| Arcadia-Designs Group Ltd | Professional & scientific | 2024 |
| Arcadian Accounting Ltd | Professional & scientific | 2013 |
| Arcadis Engineers Ltd | Professional & scientific | 2022 |
| Arcan Systems Ltd | Transport & logistics | 2024 |
| Arcane Acres Limited | Real estate | 2021 |
| Arcbaygroup Trading Ltd | Professional & scientific | 2025 |
| Arcem Limited | Professional & scientific | 2022 |
| Arcforce Engineering Services Limited | Manufacturing | 2012 |
| Arch Vision Properties Ltd | Real estate | 2022 |
| Archer and Moon Holdings Limited | Real estate | 2021 |
| Archer and Moon Property Limited | Real estate | 2021 |
| Archer Corporation Limited | Wholesale & retail | 2024 |
| Archers Health Club Limited | Arts & recreation | 2000 |
| Architectural Metals Limited | Manufacturing | 2001 |
| Architectural Profiles Limited | Construction | 1982 |
| Archive Building Limited | Real estate | 2025 |
| Archmore Homes Ltd | Hospitality | 2014 |