| Astro Property Group Ltd | Real estate | 2025 |
| Asturalgo Limited | Administrative & support | 2011 |
| Astute Recruitment Group Limited | Administrative & support | 2016 |
| Astute Technical Recruitment Limited | Administrative & support | 2006 |
| Asus Holdings Ltd | Real estate | 2018 |
| AT Mortgage Consultants Ltd | Financial services | 2021 |
| AT Solar Contractors Limited | Construction | 2023 |
| AT Your Service Dining Limited | Hospitality | 2021 |
| Atcost Aluminium Limited | Professional & scientific | 1997 |
| Atcost Window Systems Limited | Construction | 2022 |
| ATD Cleaning Solutions Ltd | Administrative & support | 2025 |
| ATE Electrical Contractors Limited | Construction | 2017 |
| Atheldene Properties Ltd | Real estate | 2023 |
| Athena South Ltd | Construction | 2024 |
| Athletic Performance & Therapy Ltd | Health & social care | 2026 |
| Atkins & Winkles Construction Ltd | Construction | 2017 |
| Atkins House Renovations Ltd | Real estate | 2022 |
| Atkinson's Glass & Mirror Centre Ltd | Administrative & support | 2003 |
| Atlanta Garage Ltd | Wholesale & retail | 2020 |
| Atlantis Cleaning Solutions Ltd | Administrative & support | 2020 |
| Atlas Construction & Design Ltd | Construction | 2025 |
| Atlas Ventures Group Limited | Other services | 2017 |
| ATM Fencing & Landscaping Ltd | Construction | 2024 |
| ATM Services Group Ltd | Professional & scientific | 2019 |
| Atoc HOL Limited | Professional & scientific | 2014 |
| Atom Investment Partners Ltd | Real estate | 2018 |
| Atomize Ltd | Construction | 2021 |
| Atrium Southern Gate Ltd | Real estate | 2025 |
| ATS Cleaning Services Ltd | Administrative & support | 2023 |
| Attache Digital Group Ltd | Information & communication | 2025 |
| Attalmajeed Ltd | Wholesale & retail | 2024 |
| Attic Conversions Hampshire Limited | Construction | 2016 |
| Attwood Plumbing & Heating Limited | Construction | 2021 |
| Atwwodhr Ltd | Administrative & support | 2024 |
| Audri Limited | Wholesale & retail | 2024 |
| AUM Retail Limited | Wholesale & retail | 2014 |
| Aunpharma Limited | Wholesale & retail | 2010 |
| AUR Transfers Ltd | Transport & logistics | 2025 |
| Aura Custom Solutions Limited | Construction | 2000 |
| Aura Fabric Engineering & Consultancy Limited | Construction | 2022 |
| Aurapicks Ltd | Wholesale & retail | 2024 |
| Aurel Construction Ltd | Construction | 2016 |
| Auriol Holdings Ltd | Real estate | 2025 |
| Aurlo Telecoms Surveying Limited | Information & communication | 2024 |
| Aurora for YOU Ltd | Professional & scientific | 2024 |
| Aurora Fragrance Ltd | Manufacturing | 2024 |
| Aurora New Dawn Ltd | Other services | 2011 |
| Austin Chessell Limited | Professional & scientific | 2019 |
| Austin Engineering and Property Ltd | Real estate | 2017 |
| Authentic Systems Limited | Information & communication | 1996 |
| Auto Innovations (Southampton) Ltd | Wholesale & retail | 2025 |
| Auto Integrate Group Limited | Information & communication | 2019 |
| Auto Integrate Ltd | Professional & scientific | 2013 |
| Auto Wash Ltd | Wholesale & retail | 2023 |
| Autofella Ltd | Wholesale & retail | 2025 |
| Autolux Car Sale Ltd | Wholesale & retail | 2025 |
| Automate-Tech Ltd | Hospitality | 2022 |
| Automated Control Services Ltd | Manufacturing | 1998 |
| Automateghana Ltd | Information & communication | 2025 |
| Automatic Door Installations Limited | Construction | 2024 |
| Automobile Flooring Ltd | Administrative & support | 2024 |
| Avalanche Resources Limited | Professional & scientific | 2010 |
| Avantgarde Marine Limited | Wholesale & retail | 2026 |
| Avasa Ltd | Real estate | 2017 |
| Avelis Interactive Ltd | Information & communication | 2025 |
| Avenue Dental Care Limited | Health & social care | 2014 |
| Avenue Spice Limited | Hospitality | 2018 |
| Avic Health Ltd | Health & social care | 2023 |
| Avisa Limited | Professional & scientific | 1998 |
| Avocado Groundworks Ltd | Construction | 2020 |
| Avonmore Property Consultants Limited | Administrative & support | 2003 |
| AW Asset Holding Ltd | Real estate | 2024 |
| AW Innovations Ltd | Arts & recreation | 2024 |
| Awaydaysproperties Limited | Hospitality | 2024 |
| AWF Utilities Ltd | Construction | 2021 |
| AWL Carpentry & Developments Limited | Construction | 2016 |
| AXE Capital Pluk Ltd | Real estate | 2023 |
| Axis Associates Limited | Real estate | 2016 |
| Axis Design Limited | Administrative & support | 2015 |
| Axis Workplace Technology Ltd | Information & communication | 2025 |
| Axyn Limited | Information & communication | 2025 |
| Aycan Shop Ltd | Wholesale & retail | 2022 |
| Ayres Minibuses Ltd | Transport & logistics | 2021 |
| Ayya Technology Ltd | Information & communication | 2023 |
| Azamats Investments Limited | Hospitality | 2025 |
| AZD Properties Limited | Hospitality | 2025 |
| Azimar Shipping Ltd | Transport & logistics | 2024 |
| Azizi Carparts Ltd | Wholesale & retail | 2026 |
| Azmar Barber Limited | Other services | 2020 |
| Aztec Elite Construction Ltd | Construction | 2024 |
| Aztec Services Southern Ltd | Construction | 2021 |
| Aztecs of London Ltd | Wholesale & retail | 2020 |
| Azui Limited | Information & communication | 2018 |
| B & W Contracting Services Limited | Construction | 2020 |
| B & B Barbers Ltd | Other services | 2006 |
| B & H Hand Carwash Ltd | Administrative & support | 2025 |
| B B S Property Investment Limited | Real estate | 2016 |
| B C Building and Carpentry Ltd | Manufacturing | 2022 |
| B Grade Hub Ltd | Wholesale & retail | 2025 |
| B Johnson Roofing Ltd | Construction | 2022 |