| Aldon B&C Limited | Construction | 2013 |
| Alea Iacta EST Limited | Financial services | 2024 |
| Alex Willson Consulting Limited | Professional & scientific | 2015 |
| Alexander Forster Garden Excellence Ltd | Health & social care | 2014 |
| Alexandropoulou Ltd | Health & social care | 2019 |
| Alisamara Ltd | Wholesale & retail | 2020 |
| Alison Bateman Consultancy Ltd | Education | 2024 |
| ALK Consultants Ltd | Professional & scientific | 2026 |
| Alliance Business Centers Network Limited | Professional & scientific | 2005 |
| Allium Consulting Group Limited | Professional & scientific | 2024 |
| Allium Global Group Limited | Other services | 2023 |
| Alovest Financial Holdings Limited | Real estate | 1953 |
| Alphabetical Order of Lebanon | Professional & scientific | 2019 |
| Alt*Ego Ltd | Manufacturing | 2022 |
| Alternate Construction Limited | Construction | 1990 |
| AM Finance Consulting Limited | Professional & scientific | 2024 |
| Amante Capital Ltd. | Hospitality | 2022 |
| Amante Holdco Ltd. | Financial services | 2022 |
| Amardillo 101 Limited | Administrative & support | 2016 |
| Amayse Ltd | Professional & scientific | 2008 |
| Amber Clothing Co. Limited | Wholesale & retail | 2004 |
| Ambleside Properties Limited | Real estate | 1987 |
| Ambleside Property Investment Company | Real estate | 1958 |
| Amedia Productions Ltd. | Information & communication | 2018 |
| Amel Trading Ltd | Financial services | 2021 |
| Ameyra Ltd | Information & communication | 2024 |
| Amjf Consultancy Limited | Information & communication | 2023 |
| Amjf Holdings Limited | Real estate | 2024 |
| Amor Entertainment Ltd | Wholesale & retail | 2023 |
| Analogue Technologies International Limited | | 1992 |
| Ancaster (UK) Limited | Real estate | 2024 |
| Ancaster Investments (UK) Ltd | Financial services | 2011 |
| Andantino Asset Management Limited | Administrative & support | 2016 |
| Anderson Court Developments Limited | Real estate | 1984 |
| Andrew Morien Hill Builders Ltd | Construction | 2024 |
| Andy Bottrill Consulting Services Ltd | Administrative & support | 2024 |
| Anew Partners Ltd | Hospitality | 2022 |
| Angie Whitnell Consultancy Ltd | Information & communication | 2020 |
| Anne Gilvarry Ltd | Health & social care | 2010 |
| Anthro Intelligence Ltd | Information & communication | 2025 |
| AO and Co Properties Limited | Real estate | 2022 |
| AP Ventures Co-Investment I GP LLP | | 2018 |
| AP Ventures Co-Investment I LP | | 2018 |
| AP Ventures Co-Investment II GP LLP | | 2018 |
| AP Ventures Co-Investment II LP | | 2018 |
| AP Ventures Co-Investment III GP LLP | | 2023 |
| AP Ventures Co-Investment III LP | | 2023 |
| AP Ventures Fund I GP LLP | | 2018 |
| AP Ventures Fund I LP | | 2018 |
| AP Ventures Fund II GP LLP | | 2018 |
| AP Ventures Fund II LP | | 2018 |
| AP Ventures Fund III GP LLP | | 2023 |
| AP Ventures Fund III LP | | 2023 |
| AP Ventures Hydrogenious Follow-On I LP | | 2023 |
| Apex E International Ltd | Wholesale & retail | 2026 |
| Apollo Real Estates Limited | Real estate | 2005 |
| Apolo Heating and Plumbing Limited | Construction | 2017 |
| Apprentico Ltd | Extraterritorial | 2007 |
| Aquilar Limited | Manufacturing | 2000 |
| Aquitron Limited | Professional & scientific | 2002 |
| Arbourne Developments Limited | Construction | 2022 |
| Arbrook Land Limited | Real estate | 2015 |
| ARC Associates London Limited | Real estate | 2016 |
| Arche Investments Ltd | Professional & scientific | 2017 |
| Archemy (UK) Limited | Professional & scientific | 2013 |
| Architects CHL Limited | Professional & scientific | 2013 |
| Architecture by Mulroy Ltd | Professional & scientific | 2022 |
| Arden & Rose Procurement Consultants Ltd | Other services | 2023 |
| ARF Build Ltd | Construction | 2025 |
| Arisma Limited | Professional & scientific | 2008 |
| Aritaur Accountancy Services Ltd | Professional & scientific | 2021 |
| Armfield Molesey Limited | Real estate | 1973 |
| Armfield Retail Ltd | Construction | 2019 |
| Armorum Partners LLP | | 2023 |
| Arone Consulting Ltd | Information & communication | 2024 |
| Arproma Limited | Construction | 2021 |
| Arras Property Services Ltd | Administrative & support | 2019 |
| ARTCO26 Limited | Arts & recreation | 2026 |
| Arthur Ellis Garden Management Limited | Administrative & support | 2026 |
| Arthur Lorcan Group Ltd | Professional & scientific | 2026 |
| Artificial Intelligence Rights Ltd | Professional & scientific | 2023 |
| Artiologie Ltd | Wholesale & retail | 2021 |
| Artreum Consulting Limited | Real estate | 2021 |
| Artugo Ltd | Extraterritorial | 2014 |
| Arugam Bay Ltd | Professional & scientific | 2024 |
| ASB International Ltd | Wholesale & retail | 2025 |
| Ascot Developments Limited | Real estate | 2011 |
| Ashburnham Park Management Company Limited | Households | 1987 |
| Ashdown Consultants Limited | Information & communication | 2025 |
| Ashton Place (Claygate) Limited | Households | 2009 |
| Aslt Ltd | Information & communication | 2024 |
| Aspire Building Services and Solutions Limited | Construction | 2017 |
| Astrolabium Grosvenor Street Limited | Wholesale & retail | 2022 |
| Astrolabium Ltd | Wholesale & retail | 2013 |
| Asuras Developments Limited | Real estate | 2018 |
| Asuta Limited | Administrative & support | 2016 |
| AT BD Consulting Ltd | Construction | 2024 |
| Aterra AI Ltd | Information & communication | 2025 |
| Athena IFA Ltd | Financial services | 2023 |
| Atlantic Technologies Limited | Information & communication | 2023 |