| Asof Real Estate Lettings Limited | Real estate | 2024 |
| ASP YVO Solution Ltd | Wholesale & retail | 2021 |
| Aspect Interior Concept Limited | Construction | 2001 |
| Aspect Plumbing & Heating (Sussex) Limited | Construction | 2009 |
| Aspen Concepts Limited | Manufacturing | 2006 |
| Aspen Holdings (Swindon) Ltd | Financial services | 2021 |
| Aspen Holdings (UK) Limited | Real estate | 2013 |
| Aspen Investment (UK) Limited | Real estate | 2013 |
| Aspen Lander Limited | Extraterritorial | 2011 |
| Aspen Manufacturing Limited | Manufacturing | 2015 |
| Aspen Renovations Limited | Construction | 2009 |
| Aspen Retail Interiors Limited | Manufacturing | 2003 |
| Aspirating Systems Limited | Extraterritorial | 2013 |
| Aspire Care Personnel Limited | Administrative & support | 2023 |
| Aspire Heating and Plumbing Limited | Construction | 2015 |
| Aspire Living Properties Ltd | Real estate | 2022 |
| Aspire TM Ltd | Construction | 2024 |
| Aspire Training and Recruitment Limited | Administrative & support | 2009 |
| Aspired Property Ltd | Real estate | 2022 |
| Aspro Car Leasing Ltd | Administrative & support | 2021 |
| Aspro Cars Ltd | Wholesale & retail | 2018 |
| Aspro Holdings Ltd | Financial services | 2024 |
| Assembleia DE Deus Newbury Limited | Other services | 2020 |
| Assembly Partners Ltd | Administrative & support | 2025 |
| Asset Guardian Company Limited | Financial services | 1997 |
| Asset Guardian Wills Limited | Professional & scientific | 2021 |
| Assetgen Limited | Information & communication | 1985 |
| Assisterweb Ltd | Professional & scientific | 2015 |
| Associated Care Solutions Limited | Health & social care | 2010 |
| Associated Electrical & Lighting Limited | Construction | 2001 |
| Association of Contact Lens Manufacturers Limited(The) | Other services | 1962 |
| Assured Car Sales Limited | Wholesale & retail | 2014 |
| Assured Enterprise Technology Limited | Information & communication | 2008 |
| Assured Wealth Management Limited | Financial services | 2019 |
| AST Digital Solutions Ltd | Manufacturing | 2019 |
| Astoria One Ltd | Transport & logistics | 2018 |
| Astormile Limited | Administrative & support | 1980 |
| Astra Communication Ltd | Wholesale & retail | 2018 |
| Astragen Ltd | Administrative & support | 2022 |
| Astray Records & Media Ltd | Information & communication | 2024 |
| Astro Dynamic Ltd | Information & communication | 2021 |
| Astro.Vnet Limited | Wholesale & retail | 2024 |
| Astronomer Ltd | Extraterritorial | 2025 |
| Asum Heights Ltd | Construction | 2025 |
| ASX Consulting Limited | Information & communication | 2009 |
| Asylum Coffee Limited | Manufacturing | 2024 |
| Asynch Consulting Limited | Professional & scientific | 2021 |
| AT1 Media Limited | Professional & scientific | 2009 |
| Atbshop Ltd | Wholesale & retail | 2012 |
| Atctech Consulting Ltd | Information & communication | 2024 |
| Athena Miniatures Limited | Manufacturing | 2015 |
| Athena Safety and Training Limited | Professional & scientific | 2008 |
| Athla West Limited | Administrative & support | 2025 |
| Athostrans Ltd | Transport & logistics | 2021 |
| Atlantic Vent Limited | Construction | 2017 |
| Atlas (Wiltshire) Ltd | Wholesale & retail | 2024 |
| Atlas 02 Ltd | Real estate | 2025 |
| Atlas Media Group Ltd | Information & communication | 2017 |
| Atlas Operational Consultancy Ltd | Professional & scientific | 2026 |
| Atlas Robotics UK Limited | Manufacturing | 2025 |
| Atlas Transport Solutions Ltd | Transport & logistics | 2018 |
| Atlive Ltd | Information & communication | 2017 |
| ATM Partners Limited | Professional & scientific | 2025 |
| Atmkz Karon Regal Holdings Ltd | Information & communication | 2026 |
| Atms Investment Ltd | Real estate | 2024 |
| Atom Sites Ltd | Information & communication | 2023 |
| Atomik Detail(Ing) Limited | Administrative & support | 2022 |
| Atrens Limited | Transport & logistics | 2015 |
| Atrium Gallery Limited | Wholesale & retail | 2008 |
| Atrl Ukconsulting Ltd | Information & communication | 2014 |
| Atrl Ukproperty Ltd | Real estate | 2019 |
| Attentive Healthcare Ltd | Health & social care | 2015 |
| Attica Components Holdings Limited | Professional & scientific | 2014 |
| Attica Components Limited | Manufacturing | 1994 |
| Attorney Wills Paralegals Limited | Administrative & support | 2024 |
| Atvue Ltd | Information & communication | 2025 |
| Atwoair Limited | Construction | 2026 |
| Atya Auto Ltd | Wholesale & retail | 2026 |
| AU Kuts Ltd | Other services | 2024 |
| AU Salon Ltd | Other services | 2025 |
| Audit, Risk & Compliance (ARC) Consultancy Limited | Professional & scientific | 2019 |
| Auditit Solutions Limited | Information & communication | 2015 |
| Audvara Group Ltd | Construction | 2025 |
| August UK Holdco Limited | Professional & scientific | 2012 |
| Aukrathanapon Ltd | Other services | 2017 |
| Aura Signs and Design Limited | Manufacturing | 2007 |
| Aurelia Care Ltd | Public administration | 2023 |
| Aurelius Holdings Ltd | Financial services | 2015 |
| Aurelius Resources UK Ltd | Financial services | 2021 |
| Aureole Limited | Professional & scientific | 1998 |
| Aurum Strategic Investments UK Ltd | Financial services | 2021 |
| Aurum Vision Ltd | Health & social care | 2025 |
| Ausaf RAI Ltd. | Professional & scientific | 2025 |
| Ausden Solutions Limited | Information & communication | 2023 |
| Austech Projects Limited | Professional & scientific | 2004 |
| Austin (Heating & Air Conditioning) Limited | Construction | 1974 |
| Austin Leisure Limited | Wholesale & retail | 2012 |
| Autism Swindon ABA Ltd | Health & social care | 2026 |
| Auto Asylum Windscreens Ltd | Wholesale & retail | 2021 |
| Auto Haven Cars Ltd | Wholesale & retail | 2025 |