| Appalachian Cinema Limited | Information & communication | 2021 |
| Appenlynn Limited | Households | 1983 |
| Appetite Group Limited | Manufacturing | 2015 |
| Appino Ltd | Information & communication | 2011 |
| Apple Accountancy Services Limited | Professional & scientific | 2008 |
| Apple Orchard Development Limited | Real estate | 2015 |
| Appletree Court Limited | Financial services | 2022 |
| Applied Implantology Ltd | Health & social care | 2025 |
| Applied Practice Ltd | Arts & recreation | 2026 |
| APS Holdco Ltd | Financial services | 2020 |
| APS Refurbishment Limited | Construction | 2017 |
| Apudos Ltd | Financial services | 2019 |
| Aqua Viva Catering Limited | Hospitality | 2011 |
| Aquameter Limited | Manufacturing | 1990 |
| Aquasions Limited | Professional & scientific | 2022 |
| Aquatic Development & Consultancy Limited | Agriculture & fishing | 2020 |
| Aquatic Remedies Limited | Agriculture & fishing | 2024 |
| AR & SP Properties LLP | | 2020 |
| Arae Consulting Limited | Professional & scientific | 2024 |
| ARB Associates Limited | Information & communication | 2017 |
| Arbicon International Limited | Administrative & support | 1986 |
| ARC of Joan Limited | Professional & scientific | 2025 |
| Arcap Funding Ltd | Financial services | 2017 |
| Arcap Partners Ltd | Financial services | 2015 |
| Arcati Productions Ltd | Administrative & support | 2013 |
| Arch Developments Limited | Real estate | 2021 |
| Arch Group UK Holdings Ltd | Financial services | 2023 |
| Archangel Clinic Limited | Health & social care | 2007 |
| Archive Art Advisory Ltd | Wholesale & retail | 2025 |
| Archive Design Studio Ltd | Professional & scientific | 2025 |
| Arco Iris Building Services Ltd | Construction | 2024 |
| Ardent Home Improvements Ltd | Construction | 2014 |
| Aren Props Ltd | Arts & recreation | 2024 |
| Arena Global Consulting Ltd | Professional & scientific | 2026 |
| Arena Wealth Management Limited | Financial services | 1975 |
| Argent Couriers LLP | | 2020 |
| Argentum Apothecary Limited | Manufacturing | 2011 |
| Argyll House Management Company (RTM) Limited | Professional & scientific | 2004 |
| Arial (PEO) Ltd | Administrative & support | 2026 |
| Arielaoz Consulting Limited | Professional & scientific | 2014 |
| Aries Investments Ltd | Real estate | 2015 |
| Ario Electrical Services Limited | Construction | 2017 |
| Aris Building Solutions Limited | Construction | 2019 |
| Arisco Ltd | Professional & scientific | 2000 |
| Arises Vision Ltd | Wholesale & retail | 2024 |
| ARK Health & Beauty (Retail) Limited | Wholesale & retail | 2009 |
| ARK Mechanical and Electrical Services Limited | Construction | 2013 |
| ARK Procurement Ltd | Wholesale & retail | 2023 |
| Arkaybrown Properties Ltd | Real estate | 2023 |
| Arki Design and Build Limited | Professional & scientific | 2013 |
| Arkley Developments Limited | Construction | 2025 |
| Arko Modern Bathrooms Ltd | Construction | 2023 |
| Arlini Limited | Professional & scientific | 2026 |
| Armand Limited | Wholesale & retail | 2000 |
| Armani Hotels Limited | Extraterritorial | 2018 |
| Arms Construction and Maintenance Ltd | Construction | 2025 |
| Arnavesh-J Ltd | Real estate | 2024 |
| Arnold Props Limited | Professional & scientific | 2025 |
| Arora Hospitality Ltd | Hospitality | 2019 |
| ARP Professional Investments Limited | Real estate | 2016 |
| ARP Professional Limited | Health & social care | 2015 |
| Arpino Wholesale Limited | Wholesale & retail | 2024 |
| Arranmead Limited | Manufacturing | 2013 |
| Arro Home Ltd | Real estate | 2024 |
| Art Dream Entertainment Ltd | Information & communication | 2019 |
| Art Habitat Ltd | Construction | 2015 |
| Art House Hire Ltd. | Administrative & support | 2008 |
| Art Market Minds Ltd | Administrative & support | 2013 |
| Art Motor Sales Ltd | Wholesale & retail | 2012 |
| Art of WAR Studios Ltd | Manufacturing | 2014 |
| Artan and Sons Ltd | Construction | 2017 |
| Artavia Advertising Limited | Professional & scientific | 1987 |
| Artefact Editions Ltd | Information & communication | 2012 |
| Artgrange Limited | Households | 1993 |
| Arthur Acoustics Ltd | Construction | 2020 |
| Arthur Interiors Ltd | Construction | 2014 |
| Artistique Vibe Films Limited | Information & communication | 2017 |
| Artists Alliance Ltd | Administrative & support | 2024 |
| Artmoon Delivery Limited | Transport & logistics | 2016 |
| Artnova Ltd | Professional & scientific | 2020 |
| Artodesign Ltd | Information & communication | 2025 |
| Artrim Ltd | Professional & scientific | 2026 |
| Arundel Lodge (Salisbury Avenue) Management Co. Limited | Households | 1965 |
| Arvatz Academy Ltd | Arts & recreation | 2023 |
| Arvon Ales Ltd | Hospitality | 2014 |
| Arvon Properties (London) Limited | Professional & scientific | 1951 |
| Arya's Media Ltd | Information & communication | 2013 |
| Aryan & Alya Fast Food Ltd | Hospitality | 2021 |
| Aryan & Alya Security Ltd | Financial services | 2025 |
| AS Dentistry Ltd | Health & social care | 2023 |
| AS Galactica Limited | Wholesale & retail | 2013 |
| AS Holdings Properties Limited | Real estate | 2020 |
| ASA Electrical Limited | Construction | 2006 |
| ASA Estate Agency Ltd | Real estate | 2017 |
| ASA General Builders Contractors Limited | Construction | 2018 |
| Asador Pickup Pintxos Limited | Hospitality | 2020 |
| Asantha Jayaweera Ltd | Health & social care | 2025 |
| Asap Investigations Ltd | Construction | 2024 |
| ASB Investments and Consultancy Limited | Real estate | 2017 |
| Asbv Consulting Limited | Health & social care | 2020 |