| Aqua Explorer C.I.C. | Education | 2025 |
| Aqua Guardian Limited | Extraterritorial | 2018 |
| Aquacheck Engineering H Limited | Administrative & support | 2003 |
| Aquacheck Engineering Limited | Manufacturing | 2009 |
| Aquacheck Group Holdings Limited | Financial services | 2026 |
| Aquaheat by P Coulson Ltd | Construction | 2021 |
| Aqualease Limited | Wholesale & retail | 2003 |
| Aqualung UK Distribution Limited | Wholesale & retail | 2021 |
| Aquarius Manufacturing Limited | Manufacturing | 1999 |
| Aquarius Tax Consultancy Ltd | Professional & scientific | 2010 |
| Aquidata XL Limited | Information & communication | 1997 |
| AR Associate Services Ltd | Health & social care | 2026 |
| AR Electrical Wholesale Ltd | Wholesale & retail | 2025 |
| AR Group Estates Ltd | Households | 2023 |
| AR Stars Ltd | Construction | 2022 |
| AR5 Group Limited | Hospitality | 2021 |
| ARA Elite Ltd | Wholesale & retail | 2025 |
| Arabellas Cafe Ltd | Hospitality | 2026 |
| ARABIA2U Ltd | Wholesale & retail | 2026 |
| Araktey Limited | Health & social care | 2019 |
| Arba Rental Properties Ltd | Real estate | 2022 |
| Arbabz Construction Ltd | Construction | 2017 |
| Arbazp Limited | Extraterritorial | 2022 |
| Arborsmith Limited | Administrative & support | 2015 |
| ARC Cabinets Limited | Administrative & support | 2010 |
| Arcadia Properties Ltd | Construction | 2000 |
| Archery Pro Shop Ltd | Wholesale & retail | 2026 |
| Archstone House Limited | Real estate | 2025 |
| Arctic Glass (UK) Limited | Manufacturing | 2009 |
| Arcturus Technology Ltd | Information & communication | 2017 |
| ARE Pares Ltd | Wholesale & retail | 2026 |
| Aren Medical Education Services Limited | Education | 2006 |
| Ares 2910 Ltd | Other services | 2016 |
| Arete Contracting Limited | Construction | 2024 |
| Arfaa Shop Ltd | Wholesale & retail | 2026 |
| Argand 200 Limited | Other services | 2020 |
| Argti Software & IT Solutions UK Ltd | Information & communication | 2024 |
| ARH DDM Ltd | Other services | 2023 |
| ARI Property Management Ltd | Manufacturing | 2019 |
| Arif Laheri Limited | Education | 2019 |
| Arif Properties Ltd | Real estate | 2025 |
| Arif Sovereign Limited | Real estate | 2013 |
| Arifa Patel Photography Limited | Professional & scientific | 2011 |
| Aristides Philippides Ltd | Manufacturing | 2024 |
| ARJ Consultants (UK) Ltd | Professional & scientific | 2013 |
| ARK Dog Walking Ltd | Other services | 2015 |
| ARL Bespoke Joinery Ltd | Manufacturing | 2024 |
| ARM Trading Ltd | Wholesale & retail | 2025 |
| ARM Wars International Limited | Arts & recreation | 2015 |
| Armaan a Travels Ltd | Administrative & support | 2020 |
| Armaan Akhtar Ltd | Health & social care | 2019 |
| Armaan Holdings Ltd | Financial services | 2020 |
| Armaans Takeaway Ltd | Hospitality | 2025 |
| Arna Recruitment Ltd | Construction | 2020 |
| Arnis Data Ltd | Information & communication | 2025 |
| Aromatic.Co Incense Cones Ltd | Wholesale & retail | 2026 |
| Aromatica Limited | Real estate | 2003 |
| ARP Property Solutions Limited | Real estate | 2026 |
| Arrdsbf Limited | Professional & scientific | 2011 |
| Arrow Tech Systems Limited | Professional & scientific | 2025 |
| Arshad 41 Ltd | Health & social care | 2021 |
| Arshad Healthcare Ltd | Health & social care | 2024 |
| Arsifa Residences Ltd | Real estate | 2025 |
| Arte Smiles UK Ltd | Other services | 2023 |
| Artisan Upholstery Ltd | Manufacturing | 2024 |
| Artist Alexandra Gallagher Limited | Wholesale & retail | 2022 |
| Artistry HQ Ltd | Other services | 2026 |
| Artistry Taints Ltd | Other services | 2024 |
| Arts for Mental Health Ltd | Health & social care | 2020 |
| ARU Holdings Limited | Financial services | 2020 |
| ARW Plant & Commercial Ltd | Manufacturing | 2021 |
| ARX Illud Adhd Ltd | Health & social care | 2021 |
| Arzed Properties Limited | Real estate | 2021 |
| AS & ZY Ltd | Real estate | 2025 |
| AS Blackburn Cars Ltd | Wholesale & retail | 2025 |
| AS Cars & Vans Ltd | Wholesale & retail | 2026 |
| AS Estates Holdings Ltd | Real estate | 2026 |
| AS Halal Meat Ltd | Wholesale & retail | 2024 |
| AS Private Hire Ltd | Transport & logistics | 2026 |
| ASA Hartford Promotions Limited | Construction | 1981 |
| Asad & Husnain Online Goods Private Limited | Wholesale & retail | 2026 |
| Asaf Lending Ltd | Financial services | 2016 |
| Asal Advisory Services Ltd | Real estate | 2020 |
| Asbt Holdings Limited | Wholesale & retail | 2018 |
| Asbt Warehousing Limited | Construction | 2021 |
| ASC Real Estate Investments Limited | Administrative & support | 2017 |
| ASC Seating & Interiors Limited | Manufacturing | 2022 |
| Ascendere Holdings Limited | Financial services | 2025 |
| Ascension Flooring Limited | Wholesale & retail | 2018 |
| Ascension Floors Limited | Wholesale & retail | 2018 |
| Ascot Plumbing & Heating Ltd | Construction | 2019 |
| Aseel Foods Ltd | Manufacturing | 2024 |
| ASF Sofa Frames Limited | Manufacturing | 2015 |
| ASG Pharma Consultancy Ltd | Professional & scientific | 2020 |
| ASG Pharma Consultants Ltd | Professional & scientific | 2015 |
| Asgard Tech Ltd | Information & communication | 2024 |
| Asghar & Sons Supermarkets Ltd | Wholesale & retail | 2018 |
| Asghar Foods Ltd | Hospitality | 2025 |
| ASH Energy Solutions Ltd | Other services | 2025 |
| ASH Planning Consultants Ltd | Professional & scientific | 2026 |