| AFI Sales & Marketing Ltd | Professional & scientific | 2019 |
| AG Consulting (UK) Limited | Administrative & support | 2013 |
| AG Design Architectural Services Limited | Professional & scientific | 2015 |
| Ag-I Technology Limited | Information & communication | 2010 |
| AG4U Ltd | Professional & scientific | 2022 |
| Aga&Arek Ltd | Real estate | 2025 |
| Agalex Ironing Service Limited | Other services | 2018 |
| Agentifyit Ltd | Information & communication | 2025 |
| Aggreg&Te Consultancy Ltd | Extraterritorial | 2021 |
| Agilis Safety Consultants Ltd | Professional & scientific | 2026 |
| AGJ Hire Limited | Administrative & support | 2018 |
| Agricision Limited | Agriculture & fishing | 2014 |
| Agricola Investments Limited | Financial services | 2013 |
| AHK Collective Ltd | Wholesale & retail | 2023 |
| AI4TP CIC | Professional & scientific | 2025 |
| AIM High Achieve More Ltd | Administrative & support | 2018 |
| AIM High for Autism (AH4A) CIC | Education | 2025 |
| Aimal Properties Ltd | Real estate | 2024 |
| Aintech Ltd | Information & communication | 2020 |
| Air Intelligence Ltd | Construction | 2012 |
| Airborne Precision Ltd | Education | 2024 |
| Airport Assist Ltd | Administrative & support | 2023 |
| Airway Travels Limited | Administrative & support | 2018 |
| Aisha Paris Smith Coaching Ltd | Education | 2024 |
| AJ Blythe Ltd | Health & social care | 2015 |
| AJ Training and Development Ltd | Professional & scientific | 2022 |
| AJ24 Ltd | Real estate | 2025 |
| AJB Technical Solutions Ltd | Information & communication | 2020 |
| AJE UK Wholesaling Limited | Wholesale & retail | 2025 |
| Ajellis Limited | Arts & recreation | 2024 |
| Ajellis Properties Ltd | Construction | 2015 |
| Ajlk Trading Ltd | Wholesale & retail | 2026 |
| AJS Estates Management Ltd | Real estate | 2025 |
| AJW Carpentry and Design Limited | Manufacturing | 2026 |
| AK and RK Limited | Hospitality | 2016 |
| AK Barber Maidenhead Ltd | Other services | 2018 |
| AKA Worldwide Limited | Wholesale & retail | 2011 |
| Akar Ltd | Real estate | 2025 |
| Akehurst Pubs Ltd | Hospitality | 2018 |
| Aketta Limited | Professional & scientific | 2016 |
| AKH Property Investments Limited | Real estate | 2023 |
| Akhtar Services (HW) Limited | Real estate | 2013 |
| Akkus Consultants Limited | Information & communication | 2011 |
| AKM Automotive Ltd | Wholesale & retail | 2024 |
| Akshara Traders Ltd | Wholesale & retail | 2022 |
| Aktyv Sports Ltd | Professional & scientific | 2026 |
| AL Dente Oxford Limited | Hospitality | 2020 |
| AL Jaleel Pharma Services Ltd | Other services | 2016 |
| AL Quick Limited | Manufacturing | 1941 |
| Alan Beattie Consultancy Limited | Professional & scientific | 2014 |
| Alastair Hill Associates Limited | Professional & scientific | 2004 |
| Alastair Little Food Limited | Hospitality | 2017 |
| Alastair Mcivor Training Limited | Professional & scientific | 2009 |
| Albadene Limited | Administrative & support | 2024 |
| Albadore Bishop Limited | Administrative & support | 2010 |
| Albamore Ltd | Wholesale & retail | 2022 |
| Albanway Limited | Wholesale & retail | 2003 |
| Albio AI Ltd | Information & communication | 2026 |
| Alcm Consulting Ltd | Professional & scientific | 2023 |
| Aldabra Limited | Administrative & support | 1999 |
| Aldred and Hopkins Young Limited | Construction | 2005 |
| Alemus Limited | Professional & scientific | 2013 |
| Alesandese Limited | Real estate | 2015 |
| Alex Buckner Golf Ltd | Arts & recreation | 2020 |
| Alex Sterling Ltd. | Real estate | 2016 |
| Alexander Devine Children's Cancer Trust | Health & social care | 2006 |
| Alexander Graphics Limited | Professional & scientific | 2003 |
| Alexandrov Logistics Ltd | Transport & logistics | 2020 |
| Alfie Douglas Limited | Manufacturing | 2012 |
| Alfonc Landscaping Service Ltd | Construction | 2026 |
| Alhaq Properties Ltd | Real estate | 2025 |
| ALI ALL Services Ltd | Administrative & support | 2022 |
| Ali's Cuts Limited | Other services | 2024 |
| Alicia Cavanagh Associates Limited | Professional & scientific | 2011 |
| Alipour Property Ltd | Real estate | 2024 |
| Alistair Bullen & Associates Limited | Professional & scientific | 1990 |
| Alix Slater Consultancy & Training Ltd | Arts & recreation | 2010 |
| Alix Wheeler Coaching Limited | Other services | 2022 |
| Aliyara Ltd | Wholesale & retail | 2026 |
| Alkindi Medical Ltd | Professional & scientific | 2021 |
| ALL in One Healthcare Limited | Public administration | 2025 |
| ALL Knight Makes Ltd | Arts & recreation | 2024 |
| ALL Round Engineering Limited | Manufacturing | 1998 |
| ALL the Things Ltd | Professional & scientific | 2024 |
| Allam Trading Ltd | Information & communication | 2026 |
| Allenby Associates Limited | Information & communication | 2009 |
| Allied Financial Group Ltd | Financial services | 2025 |
| Allonex Limited | Wholesale & retail | 2024 |
| Allports Oakley Cars Limited | Transport & logistics | 2024 |
| Alma Real Estate Consultancy Limited | Professional & scientific | 2019 |
| Almendra Europe (UK) Limited | Wholesale & retail | 2021 |
| Almond IT Consulting Limited | Information & communication | 2002 |
| Alnylam UK Holdings Limited | Manufacturing | 2024 |
| Alnylam UK Limited | Professional & scientific | 2014 |
| Alpasha Lounge Maidenhead Ltd | Hospitality | 2026 |
| Alpha Aluminium Ltd | Manufacturing | 2003 |
| Alpha Flooring (UK) Ltd | Construction | 2005 |
| Alpha Indigo Limited | Professional & scientific | 2015 |
| Alpha Interim Services Limited | Information & communication | 2007 |
| Alpha Lifting Ltd | Construction | 2023 |