| Assert Investment Ltd | Wholesale & retail | 2021 |
| Asseter Building Property Ltd | Construction | 2023 |
| Assets AS Ltd | Real estate | 2025 |
| Assign US Ltd | Administrative & support | 2022 |
| Assist With Directories Limited | Professional & scientific | 2024 |
| Associated Installations Limited | Construction | 2005 |
| Assured Advances Limited | Professional & scientific | 1996 |
| Assured Recruitment Ltd | Administrative & support | 2024 |
| Assured Water Treatment Ltd | Professional & scientific | 2019 |
| Assuretech Limited | Information & communication | 2025 |
| Asterix Business Solutions Ltd | Wholesale & retail | 2023 |
| Asticia Limited | Real estate | 2015 |
| Aston Estates (UK) Ltd | Real estate | 2012 |
| Aston Heating Limited | Construction | 1964 |
| Aston RS Limited | Administrative & support | 2024 |
| Aston Solutions Limited | Extraterritorial | 2014 |
| Astra Private Ventures Ltd | Real estate | 2024 |
| Astratech Buildco Ltd | Construction | 2023 |
| Astrodental Holdings Limited | Financial services | 2021 |
| Astrodental LLP | | 2021 |
| Astrosync Ltd | Information & communication | 2024 |
| Astrum Multi Academy Trust | Education | 2017 |
| Asuam Ltd | Health & social care | 2021 |
| Asuworn Consultants Limited | Administrative & support | 2017 |
| AT ALL Limited | Professional & scientific | 2026 |
| AT Location Limited | Real estate | 2017 |
| ATA (UK) Limited | Financial services | 2010 |
| ATA Supermarket Ltd | Wholesale & retail | 2018 |
| Atara Hair Limited | Other services | 2025 |
| Ateb Services Ltd | Professional & scientific | 2018 |
| ATG Crown Limited | Health & social care | 2019 |
| Athena Building & Landscaping Ltd | Construction | 2023 |
| Athiveera Limited | Real estate | 2017 |
| Athletefit Limited | Education | 2015 |
| Athleticfit UK Limited | Information & communication | 2011 |
| Athlite Co Limited | Wholesale & retail | 2025 |
| Athona Clinical Services Limited | Administrative & support | 2011 |
| Athona Doctors Limited | Health & social care | 2011 |
| Athona Education Limited | Education | 2017 |
| Athona Health Limited | Health & social care | 2011 |
| Athona Limited | Administrative & support | 2003 |
| Athona Trustee Company Limited | Administrative & support | 2024 |
| Atiba Galaxy Ltd | Health & social care | 2013 |
| Atila CPD Limited | Transport & logistics | 2014 |
| Atim Traders Ltd | Wholesale & retail | 2026 |
| ATK Foods Ltd | Hospitality | 2026 |
| Atkins Custom Builds Ltd | Construction | 2021 |
| Atkins Homes Ltd | Households | 2024 |
| Atkins Waste Division Ltd | Water & waste | 2026 |
| Atlant Builders Ltd | Construction | 2019 |
| Atlant Construction Limited | Construction | 2017 |
| Atlant Joinery Ltd | Construction | 2011 |
| Atlantex Services Ltd | Other services | 2013 |
| Atlantic Care Group Ltd | Administrative & support | 2018 |
| Atlantic Chambers Ltd | Real estate | 2025 |
| Atlantis Partners Limited | Professional & scientific | 2015 |
| Atlas 2014 Limited | Real estate | 2024 |
| Atlas Aero Metals Limited | Wholesale & retail | 2025 |
| ATM Enterprises Limited | Construction | 2015 |
| ATM Impex Limited | Wholesale & retail | 2018 |
| Atmaa Properties Ltd | Real estate | 2025 |
| Atom 1 Ltd | Wholesale & retail | 2015 |
| Atom FIX Ltd | Construction | 2026 |
| Atoz Consulting and Recruitment Services Ltd | Information & communication | 2023 |
| ATP Construction Ltd | Construction | 2019 |
| ATP FIX Ltd | Construction | 2015 |
| ATR Car Rentals Ltd | Administrative & support | 2024 |
| ATR Healthcare Group Ltd | Administrative & support | 2026 |
| ATS Consultant Limited | Information & communication | 2024 |
| ATS Medics Limited | Health & social care | 2020 |
| ATS Trading Limited | Transport & logistics | 2019 |
| Atsi Holdings Ltd. | Real estate | 2025 |
| Atsi Homes Ltd. | Real estate | 2025 |
| Attreed Properties Limited | Real estate | 2020 |
| Attwool Imaging Ltd | Professional & scientific | 2012 |
| ATV Realtors Ltd | Real estate | 2024 |
| ATW Carpentry and Design Ltd | Manufacturing | 2024 |
| Aubrey Creative Limited | Arts & recreation | 2023 |
| Audita Group Ltd | Extraterritorial | 2015 |
| AUK Inc Ltd | Other services | 2013 |
| AUM Pharma Consultancy Limited | Professional & scientific | 2016 |
| AUN Enterprises Ltd | Information & communication | 2025 |
| Aura AI Advisory Ltd | Professional & scientific | 2026 |
| Aura Naturale Limited | Construction | 2021 |
| Aura Portfolio Ltd | Real estate | 2026 |
| Aura Romford Ltd | Other services | 2024 |
| Auraalcove Limited | Wholesale & retail | 2024 |
| Aurae London Ltd | Other services | 2021 |
| Aurafit Limited | Wholesale & retail | 2025 |
| Auralyze.Ai Ltd | Education | 2023 |
| Aure Beauty Supply Limited | Wholesale & retail | 2025 |
| Aurea London Apparal Ltd | Wholesale & retail | 2026 |
| Aurelia Moss Ltd | Manufacturing | 2026 |
| Aurictime Limited | Wholesale & retail | 2025 |
| Auriens Gate Investment Ltd | Construction | 2015 |
| Auriga Software Limited | Information & communication | 2021 |
| Aurinko Construction Services Ltd | Construction | 2022 |
| Aurion Property Management Ltd | Real estate | 2025 |
| Aurixor Ltd | Professional & scientific | 2026 |
| Aurora & Elona Ltd | Real estate | 2018 |