| Abbey Hill Self Drive Limited | Information & communication | 1987 |
| ABCDE1 Limited | Manufacturing | 1982 |
| Abcsky Ltd | Administrative & support | 2020 |
| Aberdare Limited | Construction | 2016 |
| ABG Accountancy Limited | Real estate | 2007 |
| Abimar Limited | Real estate | 2021 |
| Abnovo Ltd | Professional & scientific | 2007 |
| Abradley Ltd | Health & social care | 2016 |
| Abstract Plans Ltd | Professional & scientific | 2018 |
| AC Bowzyk Consulting Limited | Wholesale & retail | 2021 |
| AC Heritage Ltd | Extraterritorial | 2007 |
| AC Idata Limited | Information & communication | 2021 |
| AC Sports Holidays Ltd | Administrative & support | 2023 |
| Acacia Growth Limited | Real estate | 2022 |
| Academy Two Ltd | Other services | 2001 |
| Acamar Limited | Wholesale & retail | 2005 |
| ACC Aviation Group Limited | Other services | 2014 |
| ACC Aviation Limited | Administrative & support | 2009 |
| Access ALL Areas (GB) Limited | Administrative & support | 2008 |
| Access Oral Surgery Ltd | Health & social care | 2026 |
| Accolade Wines Pension Trustees Limited | Other services | 1963 |
| Accounting AS YOU Go Limited | Professional & scientific | 2018 |
| Accounting Fore YOU Ltd | Professional & scientific | 2020 |
| Accumulus Consulting Limited | Financial services | 2001 |
| Accumulus Wealth Management Limited | Financial services | 2016 |
| Acdr Group Limited | Construction | 2023 |
| Ace Holiday Property Ltd | Hospitality | 2025 |
| Acer Treasury Solutions Ltd | Information & communication | 2017 |
| Acka Limited | Real estate | 2015 |
| Aconcagua Partners LLP | | 2017 |
| Acorn Psychiatry Ltd | Health & social care | 2022 |
| Acorn Reflow Ltd | Other services | 2017 |
| Acoustic Consultancy Ltd | Wholesale & retail | 2024 |
| Acro Builds Ltd | Construction | 2024 |
| Acstar Limited | Administrative & support | 2017 |
| ACT 5 Ventures UK Ltd | Professional & scientific | 2023 |
| Activate Fitness & Padel Retreats Limited | Arts & recreation | 2025 |
| Active Breakdown Recovery Limited | Wholesale & retail | 2018 |
| Active Management Property Solutions Ltd | Construction | 2016 |
| Active Sports Academy Ltd | Education | 2019 |
| Acton Grove Catering Ltd | Hospitality | 2007 |
| Acton House Limited | Real estate | 1994 |
| Acts Churches UK | Other services | 2018 |
| Actual Solutions (UK) Limited | Administrative & support | 1997 |
| Acue Ltd | Information & communication | 2020 |
| Adalit Limited | Professional & scientific | 1992 |
| Adam COX Fitness Ltd | Arts & recreation | 2022 |
| Adanna Limited | Construction | 2023 |
| Adaptable Living Ltd | Construction | 2017 |
| Adara Homes Limited | Real estate | 2021 |
| ADG Sport Consultancy Ltd | Professional & scientific | 2018 |
| Admongrel Ltd | Information & communication | 2017 |
| Adrian Properties Limited | Construction | 1947 |
| Adrian Wheeler & Co. Limited | Professional & scientific | 1976 |
| Adrimar Ltd | Wholesale & retail | 2020 |
| Advanced Cctv Technologies Limited | Professional & scientific | 2007 |
| Advanced Infrastructure Limited | Information & communication | 2013 |
| Advanced Ophthalmic Systems Ltd | Professional & scientific | 2020 |
| Advanse Limited | Professional & scientific | 2024 |
| Advantage Utilities Limited | Energy | 2001 |
| Advantage Water Limited | Other services | 2017 |
| ADVOC8SE Global Ltd | Administrative & support | 2025 |
| Aesthetic Events Ltd | Health & social care | 2019 |
| AET Construction Limited | Construction | 2010 |
| Africa Bees Limited | Information & communication | 2018 |
| Africa OIL Week Limited | Administrative & support | 2024 |
| Afromufasa Ltd | Hospitality | 2019 |
| Afton Fitness Limited | Arts & recreation | 2011 |
| AG Prime Ltd | Professional & scientific | 2022 |
| AG Seeker International Freight Limited | Transport & logistics | 2018 |
| AGA Couture London Limited | Manufacturing | 2019 |
| Aggregate Solutions Limited | Construction | 2025 |
| AGH Financial Consultants Limited | Financial services | 2008 |
| Agile Thinking Spaces Limited | Financial services | 2017 |
| Agni Limited | Hospitality | 2025 |
| Agrg Limited | Real estate | 2021 |
| Agulhas Gear Holdings Limited | Financial services | 2021 |
| Agulhas Gear IP Limited | Professional & scientific | 2021 |
| AGY Consultants Limited | Information & communication | 1994 |
| AHR Halal Poultry (UK) Ltd | Wholesale & retail | 2013 |
| AHS Orthopaedics Limited | Health & social care | 2017 |
| AI Crowd Limited | Information & communication | 2026 |
| AIB Trading Group Ltd | Wholesale & retail | 2025 |
| Aidan Paul Cook Developments Limited | Professional & scientific | 2015 |
| Air Music Group Limited | Information & communication | 2025 |
| Airboe Components Limited | Administrative & support | 2006 |
| Airconditioning Services Direct Limited | Manufacturing | 2001 |
| Airozen Innovation Ltd | Information & communication | 2025 |
| Aispirant Limited | Professional & scientific | 2019 |
| AJB 11 Limited | Professional & scientific | 2023 |
| AJH Carpentry & Construction Ltd | Construction | 2023 |
| AJM Construction and Development Ltd | Construction | 2025 |
| AJM Services Complete Construction Solutions Ltd | Construction | 2016 |
| AJN Building & Maintenance LLP | | 2019 |
| AK Myrta Construction Ltd | Construction | 2018 |
| AK23 Ltd | Information & communication | 2013 |
| Akasya 520 Ltd | Construction | 2013 |
| Akasya 777 Limited | Construction | 2025 |
| AKB Capital Investments Limited | Financial services | 2017 |
| Al-Khaaliq Limited | Real estate | 2023 |