| Acton Commercial Factors Limited | Wholesale & retail | 1983 |
| Acumeus Accountants Ltd | Professional & scientific | 2022 |
| AD Smile Limited | Health & social care | 2020 |
| ADA Trading Ltd | Wholesale & retail | 2025 |
| Adam Cash Consultancy Limited | Professional & scientific | 2020 |
| Adams & Co 2019 Ltd | Households | 2020 |
| Adan Property Ltd | Real estate | 2026 |
| Adare LM Clinic UK Limited | Other services | 2024 |
| ADC Building Services Limited | Construction | 2016 |
| ADD Construction Services Limited | Construction | 2016 |
| Add-On Investments Ltd | Real estate | 2023 |
| Addexx Solutions Limited | Information & communication | 2007 |
| Addico Social Ltd | Information & communication | 2013 |
| Addisland Enterprises Limited | Financial services | 2017 |
| Addmagic Limited | Wholesale & retail | 2025 |
| Adds Healthcare Limited | Health & social care | 2019 |
| Adelaide Properties ( Harrow ) Ltd | Real estate | 2025 |
| Adelaide Properties (Chesham) Limited | Real estate | 2026 |
| Adele Barnett Ltd | Extraterritorial | 2023 |
| Adele Morris (Optical Services) Ltd | Health & social care | 2013 |
| Adelly House Ltd | Construction | 2025 |
| Adevco Limited | Wholesale & retail | 2009 |
| Adhya Consulting Ltd | Information & communication | 2024 |
| Adhya Logistics Limited Limited | Transport & logistics | 2024 |
| Adikted Ltd | Wholesale & retail | 2023 |
| Adis Group Ltd | Construction | 2020 |
| ADR Constructions Drylining Ltd | Construction | 2022 |
| Adrienne M Flanagan Limited | Health & social care | 2017 |
| Adroit Global Ltd | Information & communication | 2004 |
| ADS Midlands Limited | Wholesale & retail | 2012 |
| ADS RE Holdings Limited | Real estate | 2017 |
| ADS RE Limited | Real estate | 2015 |
| Adva Group Limited | Financial services | 2020 |
| Adva Specialty Limited | Financial services | 2020 |
| Advance Cars Warwick Limited | Transport & logistics | 2018 |
| Advanced Centre of Excellence (Ace) Limited | Health & social care | 2017 |
| Advanced Footcare Group Limited | Health & social care | 2026 |
| Advanced Medical Care Ltd | Health & social care | 2026 |
| Advayd UK Solutions Ltd | Professional & scientific | 2024 |
| Advent Data Solutions Ltd | Information & communication | 2009 |
| ADY & Sons Group Ltd | Construction | 2025 |
| ADY Construction Services Ltd | Construction | 2025 |
| Adymarin Plumbing and Heating Limited | Construction | 2015 |
| Adytab Limited | Construction | 2015 |
| Aeditions Limited | Other services | 2019 |
| Aegis Life Financial Services Limited | Financial services | 2018 |
| Aeroflex Technologies Ltd | Manufacturing | 2026 |
| Aerofoam Limited | Manufacturing | 1989 |
| Aerofoam Properties Limited | Administrative & support | 2019 |
| Aesthetics by DR Rhea Ltd | Health & social care | 2022 |
| AF Beauty Services Limited | Other services | 2017 |
| Afghan British Council | Education | 2024 |
| AFH Capital Ltd | Professional & scientific | 2025 |
| African Democratic Congress (ADC - UK) International Limited | Professional & scientific | 2025 |
| Afrock International Ltd | Mining & quarrying | 2023 |
| After Dark Evening Wear Ltd | Wholesale & retail | 2012 |
| After Dark Party Limited | Administrative & support | 2011 |
| Afterbridge Limited | Households | 1989 |
| AG Associates Limited | Real estate | 2017 |
| AG Home Investments Limited | Real estate | 2019 |
| AG Technology Investment UK Ltd | Information & communication | 2008 |
| Agave Advice Ltd | Professional & scientific | 2026 |
| AGC Business (UK) Limited | Financial services | 2025 |
| AGE One Limited | Arts & recreation | 1996 |
| Agem Consulting Ltd | Professional & scientific | 2024 |
| AGF Recruiting Limited | Administrative & support | 2021 |
| Agile Chameleon Limited | Professional & scientific | 2013 |
| Agile Consultancy Limited | Information & communication | 2006 |
| Agilityphysio Ltd | Health & social care | 2023 |
| Agra IT Solutions Ltd | Information & communication | 2018 |
| Agricultural Ltd | Administrative & support | 2024 |
| AH Windows & Doors Ltd | Construction | 2023 |
| AHB Pursuit Ltd | Health & social care | 2025 |
| AHB Treetop Consulting Ltd | Professional & scientific | 2023 |
| Ahismo Ltd | Financial services | 2024 |
| AHK Assets Ltd | Information & communication | 2026 |
| AHZ Builders & Decorators Ltd | Construction | 2026 |
| AI Regulatory Solutions Limited | Information & communication | 2023 |
| Aidedeinnovation Ltd | Information & communication | 2024 |
| Aidenpro Limited | Financial services | 2013 |
| Aidos Capital Limited | Financial services | 2022 |
| Aimazing Properties Ltd | Real estate | 2025 |
| Air Ally Limited | Transport & logistics | 2010 |
| Airah Limited | Professional & scientific | 2019 |
| Aisn Properties(Uk) Limited | Real estate | 2014 |
| Aiveda AC Limited | Health & social care | 2023 |
| Aiveda Care Limited | Health & social care | 2017 |
| Aiveda Limited | Health & social care | 2010 |
| Aiveda ML Limited | Health & social care | 2023 |
| Aiveda SS Limited | Health & social care | 2023 |
| AJ & Sons Distribution Limited | Wholesale & retail | 2026 |
| AJ Auto Garage Limited | Wholesale & retail | 2018 |
| AJ Holdings (Egham) Ltd | Real estate | 2024 |
| AJ Services & Trading Limited | Manufacturing | 2019 |
| Ajad Ltd | Professional & scientific | 2026 |
| Ajbnetwork Ltd | Professional & scientific | 2025 |
| AJC Pharmacy Holdings Limited | Financial services | 2013 |
| Ajcb Investments Limited | Real estate | 2023 |
| Ajib London Ltd | Other services | 2015 |
| AJM Wealth Management Limited | Financial services | 2015 |