| Action Cat Ltd | Arts & recreation | 2004 |
| Active Finance Group Ltd | Financial services | 2015 |
| Active Online Marketing Group Limited | Administrative & support | 2010 |
| Active Online Marketing Technologies Ltd | Extraterritorial | 2010 |
| Active Premises Limited | Hospitality | 2025 |
| Active Resin Flooring Ltd | Construction | 2019 |
| Acton Aroma Limited | Wholesale & retail | 2019 |
| Actuate Technology Ltd | Professional & scientific | 2013 |
| Acumen Business Enterprise Limited | Professional & scientific | 2011 |
| Acumen Law Limited | Professional & scientific | 2008 |
| AD Wellness Ltd | Health & social care | 2018 |
| Ad&Ant Limited | Real estate | 2025 |
| AD2K Ltd | Information & communication | 2019 |
| Adair Development Co Ltd | Construction | 2023 |
| Adam Barnard Limited | Arts & recreation | 2002 |
| Adam Hankinson Consulting Ltd. | Professional & scientific | 2018 |
| Adam Jowett Orthodontics Ltd | Health & social care | 2022 |
| Adam Lane Limited | Financial services | 2019 |
| Adam Male Consulting Limited | Professional & scientific | 2019 |
| Adam Stower Limited | Arts & recreation | 2024 |
| Adam Virgo 19 Media Limited | Information & communication | 2021 |
| Adams Fothergill Ltd | Education | 2015 |
| Adams Locations Ltd | Professional & scientific | 2022 |
| Adams Upholstery Ltd | Administrative & support | 2011 |
| Adamspace Ltd | Professional & scientific | 2025 |
| Adapt Security and Medical Ltd | Administrative & support | 2025 |
| Adaptive Dynamics Limited | Professional & scientific | 2015 |
| Adbdyer Ltd | Wholesale & retail | 2024 |
| Add-Vance Solutions Limited | Professional & scientific | 2010 |
| Aderans UK Limited | Other services | 1973 |
| Adeta Limited | Other services | 2012 |
| Adhd Success Limited | Health & social care | 2023 |
| Adhd Support Ltd | Health & social care | 2023 |
| Adinkra Music Ltd | Arts & recreation | 2018 |
| ADL Inventory Services Limited | Administrative & support | 2013 |
| Adma Solutions Limited | Information & communication | 2011 |
| ADO IT Limited | Information & communication | 2014 |
| Adonis Hotels Ltd | Hospitality | 2022 |
| Adonis Leisure Ltd | Hospitality | 2022 |
| Adpol Holdings Ltd | Financial services | 2026 |
| Adregen Ltd | Professional & scientific | 2025 |
| Adrian Alan Limited | Wholesale & retail | 1974 |
| Adsolute Solutions Limited | Real estate | 2022 |
| Adszy Limited | Information & communication | 2026 |
| Adurleys Management Company Limited | Households | 2004 |
| ADV Jointing Ltd | Construction | 2022 |
| ADV Removals and Transport Ltd | Construction | 2025 |
| Advanced Connections Limited | Construction | 2003 |
| Advanced Consulting Network Limited | Professional & scientific | 2013 |
| Advanced Fire Engineering Ltd | Construction | 2007 |
| Advanced Restorative Dentistry Limited | Health & social care | 2026 |
| Adventure Connections Limited | Arts & recreation | 2007 |
| Adventures by Wanderfuel Ltd | Administrative & support | 2026 |
| Adventureyogi Limited | Professional & scientific | 2012 |
| Adversor LLP | | 2011 |
| Advertising & Marketing Grand Ltd | Professional & scientific | 2025 |
| Advovet Consultancy Services LLP | | 2024 |
| Aeon Wealth Ltd | Real estate | 2015 |
| Aequitas Developments Limited | Construction | 2009 |
| Aerosave Ltd | Professional & scientific | 2023 |
| Aesthetic Pods Limited | Health & social care | 2015 |
| Aesthetics by DR C Ltd | Other services | 2023 |
| AF Coaching Limited | Health & social care | 2026 |
| Afawan Limited | Wholesale & retail | 2025 |
| AFB Capital Ltd | Real estate | 2026 |
| Affilio Ltd | Information & communication | 2018 |
| Affleck Business Communications Ltd | Other services | 2015 |
| Aficom Property Maintenance Ltd | Construction | 2022 |
| Afphs Ltd | Professional & scientific | 2014 |
| Afresh Accountants Limited | Professional & scientific | 2017 |
| Afrikom Security Limited | Administrative & support | 2026 |
| Aftercare Universal Ltd | Other services | 2019 |
| Aftersbtn Ltd | Information & communication | 2026 |
| Agave Group Ltd | Administrative & support | 2023 |
| Agave Group Recruitment Ltd | Administrative & support | 2026 |
| Agees Access Grant Early Education Support CIC | Education | 2023 |
| Agenda S1 Ltd | Real estate | 2013 |
| Agentis Diagnostics Ltd | Health & social care | 2025 |
| Agentis Health Ltd | Health & social care | 2025 |
| Agentneville Ltd | Administrative & support | 2016 |
| AGF Property Holdings Ltd | Financial services | 2025 |
| Agile GXP Ltd | Information & communication | 1996 |
| Agile Property Group Limited | Real estate | 2018 |
| Agileappco. Ltd | Professional & scientific | 2015 |
| Agilis Business Solutions Limited | Professional & scientific | 2015 |
| Aglaia Road Limited | Households | 2005 |
| AGM Advisory Limited | Professional & scientific | 2024 |
| Agonda Property Limited | Real estate | 2017 |
| AGR Green Team Ltd | Professional & scientific | 2022 |
| AGR Waste Management Limited | Water & waste | 2018 |
| Agriculture UK and Spain Limited | Agriculture & fishing | 2000 |
| Agsh Ltd | Real estate | 2025 |
| AH Chicken Limited | Hospitality | 2023 |
| AHM Property Holdings Limited | Financial services | 2025 |
| Ahmadi Food Limited | Manufacturing | 2013 |
| Ahrend UK Limited | Wholesale & retail | 1998 |
| AHS Enterprises Ltd | Wholesale & retail | 2025 |
| AI Dunya Ltd | Information & communication | 2025 |
| AI Professional Services Limited | Professional & scientific | 2011 |
| Ai-First Mindset Limited | Professional & scientific | 2024 |