| Anico Ventures Limited | Financial services | 2021 |
| Anike by KAY Omoru Limited | Wholesale & retail | 2023 |
| Anike Care Limited | Health & social care | 2025 |
| Anike Consulting Ltd | Information & communication | 2024 |
| Anike Limited | Administrative & support | 2024 |
| Anomerge Limited | Administrative & support | 2019 |
| Ansar Carcare Limited | Wholesale & retail | 2026 |
| Ansco Consulting Ltd | Professional & scientific | 2024 |
| Ansmann UK Limited | Wholesale & retail | 2000 |
| Antares Group Ltd | Wholesale & retail | 2026 |
| ANTHEM777 Limited | Health & social care | 2020 |
| Anthony & Esther Medical Services Ltd | Health & social care | 2026 |
| Antinda Care Limited | Manufacturing | 2018 |
| Antof Logistics Ltd | Transport & logistics | 2026 |
| Anuli Health Limited | Health & social care | 2022 |
| Anuva Medical Limited | Health & social care | 2018 |
| ANV Home Decorating Limited | Construction | 2024 |
| ANY Color Customs Ltd | Transport & logistics | 2021 |
| AO Research Centre Ltd | Professional & scientific | 2024 |
| AOA Marine Services Limited | Transport & logistics | 2022 |
| AOA Medical Ltd | Health & social care | 2021 |
| Aoeo Healthcare Limited | Administrative & support | 2023 |
| Aolaw Ltd | Professional & scientific | 2019 |
| Aolaw Practice Ltd | Professional & scientific | 2024 |
| Aolynx Healthcare Ltd | Health & social care | 2026 |
| AOM Consults Limited | Health & social care | 2024 |
| Aonne Holdings Limited | Financial services | 2026 |
| AP Electrical Ltd | Construction | 2018 |
| AP Floors Ltd | Construction | 2022 |
| AP Sprayers Ltd | Construction | 2022 |
| APA Solutions Limited | Information & communication | 2019 |
| Apam Construction Ltd | Construction | 2022 |
| Apda Maintenance Limited | Construction | 2013 |
| Apele Consultancy Services Ltd | Administrative & support | 2021 |
| Apex Bargains Ltd | Wholesale & retail | 2014 |
| Apex Consults Limited | Professional & scientific | 2010 |
| Apex Harlow Ltd | Wholesale & retail | 2022 |
| Apex Loft Rooms Ltd | Construction | 2025 |
| Apex OIL Ltd | Wholesale & retail | 2026 |
| Apex Simulators Limited | Arts & recreation | 2025 |
| Apex Vending Solutions Ltd | Manufacturing | 2026 |
| Aplus Fire Safety Limited | Public administration | 2025 |
| Apollo Art Auctions Ltd | Wholesale & retail | 2018 |
| Applewood Harwell Limited | Households | 2020 |
| Aqua Clout Ltd | Administrative & support | 2019 |
| Aqualux Plumbing Ltd | Construction | 2024 |
| Aquarius PH Ltd | Construction | 2013 |
| Aquatherm Services Limited | Manufacturing | 2005 |
| Aquavive Springs Ltd | Health & social care | 2025 |
| Ar-Se Maldon Ltd | Hospitality | 2016 |
| Araviel Limited | Other services | 2025 |
| Arbanorth Ltd | Construction | 2014 |
| Arben Behari Ltd | Construction | 2020 |
| Arbitrage Consulting Ltd | Education | 2023 |
| ARC Contractors Ltd | Construction | 2018 |
| ARC Light Installations Limited | Construction | 2014 |
| Arcbright Electrical Limited | Construction | 2013 |
| Archyworks Ltd | Construction | 2022 |
| Arco Buildings Ltd | Construction | 2023 |
| Arcolite Ltd | Information & communication | 2022 |
| Arctic Moose Limited | Professional & scientific | 2018 |
| Arcxsol Limited | Manufacturing | 2022 |
| Arden Business Services Ltd | Professional & scientific | 2023 |
| Areloegbe Limited | Professional & scientific | 2013 |
| Arete Health Limited | Health & social care | 2023 |
| Argan Nanny Services Ltd | Health & social care | 2026 |
| Argento Systems Limited | Real estate | 2018 |
| Argentobaumhauerite Limited | Wholesale & retail | 2025 |
| Argus Property Services Limited | Real estate | 2022 |
| Aria Trans Ltd | Transport & logistics | 2025 |
| ARIA91 Ltd | Transport & logistics | 2020 |
| Arise 21 Ltd | Construction | 2020 |
| Ariyana Events Ltd. | Hospitality | 2022 |
| ARK Contour Holdings Limited | Financial services | 2015 |
| ARK Heating and Plumbing Ltd | Other services | 2018 |
| ARK Track Repairs Ltd | Construction | 2014 |
| Arkade Associates Limited | Construction | 2011 |
| Arlot Electrical Contractors Limited | Construction | 2025 |
| ARM Steel Daniel Ltd | Transport & logistics | 2018 |
| Arman Contractors Ltd | Construction | 2016 |
| Armani Cargo Services Limited | Transport & logistics | 2017 |
| Armoury Way London Ltd | Arts & recreation | 2026 |
| Armoury Way Ltd | Arts & recreation | 2025 |
| Arnold Muller Limited | | 1960 |
| Arobad Holdings Ltd | Health & social care | 2019 |
| Aroma Alchemy Vending Ltd | Manufacturing | 2025 |
| Aron Clothing and Accessories Limited | Wholesale & retail | 2022 |
| Aron Property Services Limited | Real estate | 2020 |
| Aronmultilink Limited | Manufacturing | 2015 |
| Arraffy Limited | Health & social care | 2022 |
| Arrow Electronics (UK) Limited | Wholesale & retail | 1991 |
| Arrow Electronics Limited | Financial services | 1996 |
| Arrow Nordic Financing Limited | Professional & scientific | 2023 |
| Art and Industry Limited | Real estate | 2009 |
| Art and Industry Properties Limited | Real estate | 2024 |
| Art of Freight Limited | Administrative & support | 2017 |
| Art Pack UK Ltd | Wholesale & retail | 2019 |
| Arthenella Limited | Manufacturing | 1993 |
| Artisan Building Solution Ltd | Construction | 2026 |
| Artisan Fine Art Ltd | Wholesale & retail | 2022 |