| Asset Harbour Group Holdings Limited | Financial services | 2019 |
| Asset Harbour Limited | Administrative & support | 2010 |
| Asset Wealth Advisory Limited | Financial services | 2023 |
| Assistants From a Distance Ltd | Administrative & support | 2023 |
| Association for Key Account Management Limited | Information & communication | 2024 |
| Assured Service Delivery Limited | Information & communication | 2022 |
| Assured Wills (Kent) Limited | Administrative & support | 2024 |
| Astarr Property Services Ltd | Construction | 2023 |
| Aster Horses Ltd | Agriculture & fishing | 2016 |
| Astering Capital Ltd | Financial services | 2017 |
| Asterisk Project CIC | Health & social care | 2026 |
| Aston Green Properties Ltd | Real estate | 2012 |
| Aston Spinks Survey Ltd | Professional & scientific | 2017 |
| Astoria Trading & Consulting Ltd | Extraterritorial | 2011 |
| Astra UK (Contracts) Limited | Administrative & support | 1995 |
| Astral DRY Cleaning Limited | Other services | 2023 |
| Astrauk Holdings Limited | Real estate | 2011 |
| Astride Ltd | Wholesale & retail | 2026 |
| Astromedia Technologiess Ltd | Professional & scientific | 2026 |
| Astute Professional Services Limited | Other services | 2012 |
| Asza Property Ltd | Real estate | 2022 |
| AT-8 Utilities Limited | Construction | 2018 |
| ATA Carnet Express Ltd | Public administration | 2022 |
| ATC Testing Ltd | Professional & scientific | 2016 |
| Atharier Ltd | Other services | 2025 |
| Athena Consillium Ltd | Financial services | 2013 |
| Athlex Limited | Professional & scientific | 2024 |
| Atis Supplies Ltd | Information & communication | 2010 |
| Atkeen Limited | Real estate | 1986 |
| Atlantic Print Media LLP | | 2014 |
| Atlantic RT Holdings Limited | Real estate | 2019 |
| Atlas Bagging Equipment Limited | Wholesale & retail | 2018 |
| Atlas Equity Holdings Ltd | Financial services | 2025 |
| Atlas Performance Sportswear Limited | Manufacturing | 2020 |
| Atlasd Systems Ltd | Information & communication | 2025 |
| Atlaspoint Limited | Information & communication | 2013 |
| Atolye K Ltd | Professional & scientific | 2018 |
| Atomic Frog Limited | Information & communication | 2026 |
| Atomic Holdings Ltd | Financial services | 2026 |
| Atomicity Consultancy Services Ltd | Information & communication | 2017 |
| Atomikuk Limited | Manufacturing | 2017 |
| ATR Distribution Limited | Wholesale & retail | 2023 |
| ATR Duct Services Limited | Administrative & support | 2025 |
| ATS Customs Ltd | Transport & logistics | 2026 |
| Atters Creative Services Limited | Professional & scientific | 2012 |
| ATW25 Ltd | Administrative & support | 2025 |
| AU Limited | Financial services | 2004 |
| Audio Experts Limited | Professional & scientific | 2009 |
| Auletta SOT Limited | Wholesale & retail | 1997 |
| Aura Ventures Limited | Professional & scientific | 2003 |
| Aureon Water Technologies Limited | Water & waste | 2026 |
| Aureus Trading Limited | Wholesale & retail | 1999 |
| Aurora M and E Ltd | Construction | 2024 |
| Aurorapod Ltd | Manufacturing | 2025 |
| Aurum Financial Management Limited | Financial services | 2012 |
| Aurum Innovations Ltd | Information & communication | 2021 |
| Ausfelia Limited | Health & social care | 2025 |
| Ausska Limited | Information & communication | 2021 |
| Austins Property Services & Development Ltd | Households | 2013 |
| Australasian Immigration Services Ltd | Professional & scientific | 2023 |
| Australis Distribution Limited | Wholesale & retail | 2003 |
| Authentic Timber Windows Ltd | Manufacturing | 2006 |
| Auto Shine of Ashford Ltd | Other services | 2018 |
| Autogate Systems Holdings Ltd | Financial services | 2010 |
| Autogate Systems Limited | Construction | 2007 |
| Autolife Ltd | Wholesale & retail | 2024 |
| Automated Environmental Systems (South) Limited | Manufacturing | 2007 |
| Automated Environmental Systems Holdings Limited | Financial services | 2023 |
| Automated Environmental Systems Limited | Wholesale & retail | 2013 |
| Automated-Digital Technology Limited | Transport & logistics | 2020 |
| Automotive Design & Development Limited | Wholesale & retail | 2013 |
| Automotive HR Limited | Professional & scientific | 1998 |
| Autopaintsdirect Ltd | Wholesale & retail | 2020 |
| Autovalet Direct Franchising Limited | Administrative & support | 2005 |
| AV Construction (London) Limited | Construction | 2017 |
| AV1923 Limited | Real estate | 2026 |
| Avalon Block Management Ltd | Real estate | 2022 |
| Avalon House 260 Limited | Households | 2018 |
| Avalon House Ltd | Administrative & support | 2016 |
| Avant Corporation Limited | Other services | 2018 |
| Avant-Garde Financial Advice Limited | Financial services | 2004 |
| Avanti Driving School Ltd | Education | 2026 |
| Avari Property Limited | Real estate | 2019 |
| Aveeno Holdings Ltd | Real estate | 2021 |
| Aveeno Homes Ltd | Real estate | 2017 |
| Avengers Prime Care Ltd. | Health & social care | 2015 |
| Averroes Associates Ltd | Health & social care | 2020 |
| Avershaw Properties Limited | Real estate | 2025 |
| Aviation Parts & Tools Ltd | Manufacturing | 2005 |
| Avid Web Limited | Information & communication | 2010 |
| Avington Enterprises Limited | Real estate | 2020 |
| Avlis Telecommunications and System Limited | Information & communication | 2014 |
| Avon Network Events Limited | Administrative & support | 2020 |
| Avsa Limited | Wholesale & retail | 2022 |
| Avuyile Sibuta Limited | Health & social care | 2018 |
| AW Armoury Ltd | Wholesale & retail | 2014 |
| Awaken Property Group Limited | Households | 2019 |
| Awareness on Message Limited | Professional & scientific | 2015 |
| AWE & Sonder Limited | Professional & scientific | 2023 |
| Awesome Living Ltd | Information & communication | 2023 |