| Abraham Investments Limited | Construction | 1982 |
| ABS Luton Limited | Wholesale & retail | 2021 |
| Absolum Drive & Landscapes Limited | Construction | 2013 |
| Absolute Moco Ltd | Administrative & support | 2017 |
| AC Waste Clearance Ltd | Water & waste | 2025 |
| Academic Registry Consultancy Ltd | Professional & scientific | 2024 |
| Acantha Group Limited | Wholesale & retail | 2020 |
| Acc&Tax Limited | Professional & scientific | 2010 |
| ACCESS2BOOKS Limited | Information & communication | 2013 |
| Accurate Plastering Solution Ltd | Construction | 2013 |
| Accuro Limited | Professional & scientific | 1998 |
| Aceking Consulting Ltd | Professional & scientific | 2026 |
| ACF Flooring Solutions Ltd | Construction | 2024 |
| Acora Properties Ltd | Construction | 2020 |
| Acorn Economics Ltd | Professional & scientific | 2023 |
| Acorn Leisure Homes Limited | Hospitality | 2013 |
| Acorn Management Consultants Limited | Professional & scientific | 2008 |
| ACP Automotive Limited | Transport & logistics | 2016 |
| Acquire Consultant Solutions Ltd | Professional & scientific | 2024 |
| Acsa Consulting Ltd | Professional & scientific | 2026 |
| ACT Fast Roofing and Building Ltd | Construction | 2025 |
| Action Physiotherapy Ltd | Health & social care | 2006 |
| Action This Day Kenya | Education | 2013 |
| ACTIVE8 Communities Ltd | Administrative & support | 2023 |
| Actuaria Ltd | Professional & scientific | 2022 |
| Acuity Technology Consulting Ltd | Information & communication | 2016 |
| Adamas Investment Holdings LLP | | 2021 |
| Adamesh Limited | Wholesale & retail | 2005 |
| ADD Engineering Solutions Ltd | Professional & scientific | 2026 |
| Ademconsult Limited | Information & communication | 2022 |
| Adex Holdings Limited | Financial services | 2017 |
| Adex Interiors for Industry Ltd | Construction | 1979 |
| Adlabes Company Limited | Manufacturing | 2016 |
| ADS Plumbing & Heating Services Ltd | Construction | 2017 |
| Advance Water Treatment Technologies Limited | Water & waste | 2018 |
| Advanced Breakdown Services UK Ltd | Extraterritorial | 2024 |
| Advanced Business Capital Limited | Professional & scientific | 1998 |
| Advanced Innovation and Marketing Limited | | 1990 |
| Advanced Remediation Limited | Financial services | 2021 |
| Adventurace Ltd | Administrative & support | 2021 |
| Advizar Ltd | Professional & scientific | 2024 |
| ADW Utility Solutions Ltd | Professional & scientific | 2025 |
| Adworks Design Ltd | Arts & recreation | 1999 |
| Aequiam Limited | Professional & scientific | 2012 |
| Aerios Systems Limited | Information & communication | 2012 |
| AFC Consulting (UK) Limited | Professional & scientific | 2014 |
| Affinity Sphere Limited | Information & communication | 2024 |
| Affordable Cars Luton Ltd | Wholesale & retail | 2022 |
| AG & C Limited | Manufacturing | 2019 |
| Agape Consulting Limited | Administrative & support | 2019 |
| Agas and Boilers Ltd | Construction | 2021 |
| Agency Ghost Ltd | Professional & scientific | 2019 |
| Agencypro Limited | Education | 2013 |
| Agentstorm Ltd | Information & communication | 2026 |
| Agga Trading Limited | Hospitality | 2021 |
| Agriware Ltd | Information & communication | 2025 |
| Agshopping Crew Ltd | Wholesale & retail | 2023 |
| Ahmed Taxis Ltd | Administrative & support | 2019 |
| AI POP Ltd | Transport & logistics | 2023 |
| AI Solutions Limited | Information & communication | 1995 |
| AIA Solutions Ltd | Information & communication | 2022 |
| AIM Assist Holdings Ltd | Information & communication | 2017 |
| Ainiya Limited | Wholesale & retail | 2017 |
| Aion Consulting Limited | Information & communication | 2019 |
| Airbox Fulfilment Ltd | Transport & logistics | 2017 |
| Aircraftech Ltd | Manufacturing | 2021 |
| Airluxe Management Ltd | Real estate | 2023 |
| Airsole Company Limited | Manufacturing | 2022 |
| Airtime Technology Limited | Transport & logistics | 1990 |
| Airun Limited | Information & communication | 2017 |
| Airwave Compressors Ltd | Manufacturing | 2022 |
| Aistek Limited | Information & communication | 2023 |
| AJ Installation Team Ltd | Manufacturing | 2017 |
| AJ Taste Ltd | Wholesale & retail | 2025 |
| Ajfroberts Consulting Ltd | Professional & scientific | 2023 |
| Ajiga Healthcare Ltd | Health & social care | 2024 |
| AK Accounts and Taxation Limited | Professional & scientific | 2015 |
| AK Blinds Limited | Households | 2020 |
| AK Fire Door Services Ltd | Construction | 2024 |
| AK Office Solutions Ltd | Administrative & support | 2024 |
| Akalpa Properties Limited | Real estate | 2024 |
| Akeena & Co. Limited | Wholesale & retail | 2025 |
| AKI Solutions Ltd | Wholesale & retail | 2020 |
| AKJ Consult Ltd | Construction | 2023 |
| Akki Aviation Services Limited | Professional & scientific | 2019 |
| Aksaf Ltd | Hospitality | 2022 |
| Akshchin Technologies Ltd | Information & communication | 2022 |
| Akurve Limited | Professional & scientific | 2024 |
| Al-Busttan UK Limited | Mining & quarrying | 2016 |
| Al.Shaws Ltd | Wholesale & retail | 2000 |
| Alan J Smith Limited | Professional & scientific | 2023 |
| Alazaroaie Ltd | Construction | 2025 |
| Albany Heights Management Company Limited | Households | 2005 |
| Albie Media Ltd | Arts & recreation | 2024 |
| Albion Investments Inc. Ltd | Real estate | 2020 |
| Alden Aviation Services Ltd | Transport & logistics | 2019 |
| Alder Residents Association Limited | Households | 1989 |
| Alderan Property Limited | Real estate | 2025 |
| Alede Management Ltd | Real estate | 2025 |
| Alex Brickwork Ltd | Construction | 2017 |