| Atlantis Swimwear Ltd | Wholesale & retail | 2018 |
| Atlitw Atelier Ltd. | Professional & scientific | 2021 |
| Atom Promos Ltd | Professional & scientific | 2023 |
| Atron Group Limited | Construction | 2022 |
| ATS Capital Limited | Financial services | 2023 |
| Atsyuk Limited | Wholesale & retail | 2026 |
| Attactus Limited | Real estate | 2024 |
| Atticmedia Limited | Information & communication | 2010 |
| Attract & Engage Limited | Professional & scientific | 2021 |
| Auburn Surveyors Limited | Real estate | 2022 |
| Auction Direct Flowers Limited | Administrative & support | 2013 |
| Audiimax Ltd | Wholesale & retail | 2023 |
| Augmental Games Limited | Information & communication | 2017 |
| Aura Design Events Limited | Wholesale & retail | 2008 |
| Aura Design Flowers Limited | Other services | 2008 |
| Aurea Nova Limited | Professional & scientific | 2025 |
| Aurestra Limited | Wholesale & retail | 2026 |
| Auris Autos Ltd | Wholesale & retail | 2013 |
| Aurum Palladion Investments Ltd | Financial services | 2024 |
| Austinstore Limited | Wholesale & retail | 2024 |
| Authlink Limited | Professional & scientific | 2013 |
| Autocomms Solutions Ltd | Information & communication | 2020 |
| Autohut Group Ltd | Wholesale & retail | 2017 |
| AUTOLADY.5STAR Limited | Education | 2024 |
| Automate to Scale Ltd | Professional & scientific | 2021 |
| Autosonic (PUB Division) Ltd | Administrative & support | 1998 |
| Autto Limited | Information & communication | 2016 |
| Auxilium Curo Ltd | Professional & scientific | 2020 |
| AV Alliance Media Limited | Professional & scientific | 2026 |
| AV Cargo Airlines Limited | Transport & logistics | 2013 |
| AV Jain Limited | Health & social care | 2016 |
| Avadyl Developments Ltd | Construction | 2021 |
| Avalon Abseiling Limited | Construction | 2003 |
| Avalon Access Limited | Construction | 2009 |
| Avalon Facade Fire Prevention Ltd | Construction | 2020 |
| Avalon High Ltd | Construction | 2011 |
| Avalon Laser and Wellbeing Limited | Other services | 2015 |
| Avalon Sales & Marketing Ltd | Wholesale & retail | 2025 |
| Avalon Sustainable Energy Solutions Ltd | Construction | 2010 |
| Avalonpro Group Limited | Construction | 2009 |
| Avansim International (Holdings) Limited | Financial services | 2019 |
| Avansim Ltd. | Information & communication | 2016 |
| Aveling Property Services Ltd | Real estate | 2012 |
| Avery Traffic Consultants Ltd | Professional & scientific | 2011 |
| Avet Technology Limited | Manufacturing | 2015 |
| Aviation Traders Engineering Ltd | Professional & scientific | 2006 |
| Avie Consultancy Limited | Professional & scientific | 2018 |
| Avira Properties Ltd | Construction | 2025 |
| Avoca House Hotel (Swiss Cottage) Limited | Hospitality | 1978 |
| AVR Consultants Limited | Professional & scientific | 2017 |
| AW Diamond Setting Limited | Manufacturing | 2017 |
| AW Mechanical Engineering Services Ltd | Professional & scientific | 2025 |
| AWE Consulting UK Ltd | Administrative & support | 2010 |
| Axiara Limited | Wholesale & retail | 2026 |
| Axiom Personnel Limited | Administrative & support | 2005 |
| Axioma Europe Ltd | Financial services | 2018 |
| Axionest Ltd | Hospitality | 2026 |
| AXO Services Ltd | Construction | 2018 |
| Ayub's Pink Garlic Limited | Hospitality | 2017 |
| Azariah Medical Partnerships Ltd | Health & social care | 2018 |
| Azazel Limited | Construction | 2017 |
| Azuntu Studio Ltd | Information & communication | 2018 |
| B & B Consultancy Limited | Professional & scientific | 1983 |
| B & S UK Trading Ltd | Other services | 2021 |
| B and B Essex Ltd | Other services | 2020 |
| B and K Flooring Limited | Construction | 2025 |
| B and M Builders Limited | Construction | 2010 |
| B for Barcelona Limited | Wholesale & retail | 2017 |
| B L Autos Grays Ltd. | Wholesale & retail | 2013 |
| B W Chatten LLP | | 2008 |
| B Watts Maintenance Ltd | Construction | 2025 |
| B&R Property Management Limited | Real estate | 2018 |
| B. Everett Transport Limited | Transport & logistics | 2014 |
| B. Williams Properties Ltd | Construction | 1980 |
| B.S.Estate Management Limited | Real estate | 1970 |
| B2LO Shop Limited | Administrative & support | 2012 |
| B7 Media Group Ltd | Professional & scientific | 2017 |
| Baba Swami Limited | Real estate | 2024 |
| Babos Grocery Ltd | Wholesale & retail | 2022 |
| Babushka Social Limited | Professional & scientific | 2014 |
| Babyballet Rbbc Limited | Education | 2023 |
| Backup Abseil Ltd | Professional & scientific | 2023 |
| Bacqd Media Ltd | Information & communication | 2026 |
| Badgerfox Tickets Ltd | Arts & recreation | 2023 |
| Baicoz Ltd | Other services | 2024 |
| Bailey Shopfitters Limited | Construction | 1987 |
| Baines Gardening Limited | Administrative & support | 2020 |
| Bakentry Ltd | Information & communication | 2019 |
| Baker Self-Adhesive Label Company Limited(The) | Manufacturing | 1973 |
| Bakers Catering Limited | Hospitality | 2023 |
| Bakers Court (Brentwood) Limited | Real estate | 2007 |
| Bakers Group Holdings Ltd | Financial services | 2026 |
| Bakhshi and Shirazi Holdings Ltd | Health & social care | 2022 |
| Baldwin Bros. (Engineers) Limited | Real estate | 1955 |
| Baldwin Plastic Laminates Limited | Manufacturing | 1988 |
| Baley Design and Build Ltd | Construction | 2020 |
| Balloominate Limited | Wholesale & retail | 2020 |
| Baltihouse Brentwood Ltd | Hospitality | 2024 |
| Baltimore Properties Limited | Real estate | 1989 |
| BAM BAM Sports Limited | Real estate | 2022 |