| Arnstein Associates Limited | Professional & scientific | 2015 |
| Aroa Services Ltd | Information & communication | 2018 |
| Aroeye Ltd | Information & communication | 2019 |
| Aross Property Consultancy Ltd | Real estate | 2024 |
| Arqm Development Limited | Construction | 2025 |
| Arrow Creative Limited | Arts & recreation | 2025 |
| Arrow Education HR Ltd | Administrative & support | 2025 |
| Arrowsmith Antiques Limited | Wholesale & retail | 1995 |
| Art Gym Limited | Extraterritorial | 1975 |
| Artful Gardens Ltd | Professional & scientific | 2023 |
| Arthur Elkin Skirts and Pleaters Limited | Manufacturing | 2017 |
| Artisan Electrical Services Limited | Construction | 2016 |
| Artmageddon Ltd | Other services | 2011 |
| Artmode Limited | Professional & scientific | 2022 |
| Arts Pedagogy Limited | Education | 2025 |
| Arturi and Associates Ltd | Professional & scientific | 2017 |
| AS Corporate Group Ltd | Administrative & support | 2019 |
| Asbury & Asbury Ltd | Administrative & support | 2013 |
| Ascend Coaching & Consulting Ltd | Professional & scientific | 2023 |
| Ascent Perfumes Ltd | Extraterritorial | 2011 |
| Ascot Gardens Residents Management Company Ltd | Households | 2026 |
| Ashdowne OIL & Chemical Limited | Administrative & support | 2009 |
| Ashfield House Limited | Hospitality | 1987 |
| Ashley Howard Limited | Extraterritorial | 2020 |
| Ashley Waller Auctions Ltd | Wholesale & retail | 2017 |
| Ashley Waller Limited | Wholesale & retail | 2017 |
| Ashmore IT Limited | Information & communication | 2010 |
| Ashton Tyre Specialists Limited | Wholesale & retail | 1983 |
| Asia Marketing Services Limited | Wholesale & retail | 2012 |
| Asia Technology Ventures Limited | Professional & scientific | 2021 |
| Asim 25 Limited | Professional & scientific | 2025 |
| Askbow Investments Limited | Administrative & support | 2020 |
| ASP Brand Ltd | Wholesale & retail | 2025 |
| Aspect Point Limited | Education | 2025 |
| Aspenwood Properties Limited | Real estate | 2026 |
| Aspera PM Limited | Professional & scientific | 2008 |
| Aspire Buildings Limited | Construction | 2015 |
| Asser Oakes Engineering Limited | Manufacturing | 2004 |
| Assist Virtually Limited | Administrative & support | 2021 |
| Association of Acupuncture Clinicians Ltd. | Other services | 2021 |
| AST. Redbridge Limited | Real estate | 2024 |
| Astle Estates Limited | Construction | 2023 |
| Astron Systems Ltd | Manufacturing | 2021 |
| Astrumax Limited | Wholesale & retail | 2021 |
| At&C Properties Limited | Real estate | 2015 |
| Atax (Properties) Limited | Real estate | 1975 |
| Atelier FBH Limited | Construction | 2015 |
| Atelier Group Holdings Limited | Financial services | 2019 |
| Atelier Joinery Limited | Manufacturing | 2010 |
| Athena Groundworks Limited | Administrative & support | 2006 |
| Athene Coaching Limited | Extraterritorial | 2023 |
| Atherley Thorp Limited | Wholesale & retail | 2008 |
| Athuruga Ltd | Real estate | 2018 |
| Atjt Ltd | Construction | 2024 |
| Atlantic Advisors Limited | Professional & scientific | 2011 |
| Atlantic Performance Centre Ltd | Wholesale & retail | 2003 |
| Atlas Training Club Ltd | Health & social care | 2026 |
| Atmosclear Holdings Limited | Professional & scientific | 2019 |
| Atmosclear International Ltd | Professional & scientific | 2019 |
| Atmosclear Investments Ltd | Professional & scientific | 2018 |
| Atomic Theatre Arts Limited | Arts & recreation | 2025 |
| ATS Cycles Limited | Manufacturing | 2014 |
| Attentive Carers Ltd | Health & social care | 2023 |
| Audibox Ltd | Professional & scientific | 2017 |
| Audio Security Install Limited | Wholesale & retail | 2003 |
| Audio Visual Freelance Collective Limited | Information & communication | 2022 |
| Auricane Ltd | Professional & scientific | 2023 |
| Aurora Architecture Ltd | Professional & scientific | 2025 |
| Aurora Products Limited | Manufacturing | 2013 |
| Aurro Ltd | Administrative & support | 2025 |
| Austin Design and Build Limited | Manufacturing | 2022 |
| AUT Vincam AUT Peribo Ltd | Professional & scientific | 2012 |
| Autac Assemblies Limited | Extraterritorial | 2019 |
| Autac Bespoke Limited | Extraterritorial | 2024 |
| Autac CV Limited | Extraterritorial | 2018 |
| Autac EV Limited | Extraterritorial | 2019 |
| Autac Products Limited | Manufacturing | 1964 |
| Auto Aqua Ltd | Administrative & support | 2026 |
| Auto Classica Limited | Transport & logistics | 2019 |
| Auto Drift Ltd | Wholesale & retail | 2025 |
| Auto Matrix Limited | Wholesale & retail | 2018 |
| Auto Scrap & Salvage Ltd | Water & waste | 2025 |
| Auto Tech Essentials Limited | Professional & scientific | 2012 |
| Auto-Scrap.Com Ltd | Wholesale & retail | 2025 |
| Autolearn Limited | Households | 1992 |
| Automate IQ Ltd | Information & communication | 2026 |
| Automotive Bodyfillers Limited | Manufacturing | 1996 |
| Autorola Ltd | Wholesale & retail | 1997 |
| Autovhr Limited | Administrative & support | 2025 |
| Autumnbell Limited | Professional & scientific | 2014 |
| Auxilium Conservation Ltd | Arts & recreation | 2026 |
| AVA Cad/Cam Group Limited | Information & communication | 2002 |
| Avalon Macclesfield LLP | | 2010 |
| Avant Engineering Ltd | Professional & scientific | 2007 |
| Avanti Nestings Ltd | Real estate | 2017 |
| Aventurine Management Consulting Limited | Professional & scientific | 2024 |
| Aviabridge Limited | Professional & scientific | 2021 |
| Aviation Connect Limited | Extraterritorial | 2012 |
| Aviatsiya Ltd | Manufacturing | 2022 |
| AVM Studios Ltd | Other services | 2019 |