| Alpha Brokers Limited | Financial services | 2002 |
| Alpha Contract Solutions Limited | Professional & scientific | 2024 |
| Alpha Echo Mike Ltd | Professional & scientific | 2025 |
| Alpha Sport Limited | Arts & recreation | 2019 |
| Alpha Talent Group Ltd | Other services | 2019 |
| Alternative Print Solutions Limited | Manufacturing | 2006 |
| Altitude Internet Digital Marketing Services Limited | Professional & scientific | 2014 |
| Altitude Internet Limited | Information & communication | 2014 |
| Altitude Internet Technology Limited | Information & communication | 2014 |
| Altona (Clapham) Residents Management Company Limited | Households | 2004 |
| Altrix Ltd | Professional & scientific | 2025 |
| Aluminium Pro Ltd | Manufacturing | 2021 |
| Alverton Ltd | Wholesale & retail | 2020 |
| Always Stock Ltd | Wholesale & retail | 2020 |
| AMA Anaesthesia Ltd | Health & social care | 2023 |
| Amadea Music Limited | Administrative & support | 2013 |
| Amadea Music Publishing Ltd | Information & communication | 2022 |
| Amassie Trading Ltd | Wholesale & retail | 2025 |
| Amazene Limited | Manufacturing | 2006 |
| Amber Rose Psychotherapies Ltd | Health & social care | 2021 |
| Amber Tiger Holdings Ltd | Administrative & support | 2015 |
| Ambient Concept Limited | Professional & scientific | 2008 |
| Ambient Heating Solutions Ltd | Construction | 2020 |
| Ambon Ltd | Administrative & support | 2017 |
| Ames Court Management Limited | Households | 2017 |
| AMG Global Consultancy Ltd | Professional & scientific | 2020 |
| AMG Southern Services Ltd | Construction | 2007 |
| Amho Limited | Education | 2023 |
| Amity Arts Limited | Arts & recreation | 2025 |
| Amiya Healthtech Ltd | Information & communication | 2026 |
| Amoux Limited | Professional & scientific | 2016 |
| Ampersand Associates Limited | Professional & scientific | 1990 |
| Ampersand Facilities Management Ltd | Real estate | 2025 |
| Ampersand Keystone Ltd | Construction | 2025 |
| Ampi Property Limited | Real estate | 2022 |
| Amrayvier Services Limited | Administrative & support | 2023 |
| AMX Print Limited | Manufacturing | 2003 |
| AMY Mattryan Ltd | Administrative & support | 2017 |
| AMY Nails Bishop Limited | Other services | 2025 |
| AMY Wilkes Design Ltd | Professional & scientific | 2019 |
| Amy's Nails Spa Ltd | Other services | 2019 |
| Amymattryan Properties Ltd | Real estate | 2020 |
| AN Uncommon Practice Ltd | Other services | 2025 |
| ANA 24 Logistics Limited | Transport & logistics | 2018 |
| Anacruses Associates Ltd | Professional & scientific | 2022 |
| Anagram International Ltd | Wholesale & retail | 2024 |
| Anais Pharma Ltd | Wholesale & retail | 2024 |
| Anaxi Education Ltd | Information & communication | 2023 |
| Anca Design Limited | Information & communication | 2021 |
| Ancient & Modern Glazing Limited | Construction | 1994 |
| AND Events Limited | Hospitality | 2020 |
| Andell Electrical Ltd | Construction | 2021 |
| Anderson Browne Solicitors Limited | Professional & scientific | 2010 |
| Andrew Draper Electrical (AD Electrical) Ltd | Construction | 2026 |
| Andrew Reynolds Music Ltd | Education | 2026 |
| Andrew Smith Print Limited | Manufacturing | 2015 |
| Andrew Turvey Solutions Limited | Professional & scientific | 2020 |
| Andrewmurphydesign Ltd | Professional & scientific | 2020 |
| Angel Safe Ltd | Extraterritorial | 1999 |
| Anglia Guardians Ltd | Education | 2009 |
| Anglia Pipe Tools Limited | Wholesale & retail | 2000 |
| Anglia Plant and Equipment Services Ltd | Manufacturing | 2018 |
| Anglia Properties (East Anglia) Limited | Real estate | 2025 |
| Anglo Spanish Imports Limited | Wholesale & retail | 1971 |
| Angus Limited | Real estate | 2015 |
| Animal & Scientific Consults Ltd | Professional & scientific | 2023 |
| Anjan Ltd | Health & social care | 2023 |
| Anna Mitchell Copywriting Ltd | Administrative & support | 2024 |
| Annabel Green Leadership Consulting Ltd | Professional & scientific | 2024 |
| ANR Electrical Limited | Construction | 2003 |
| Ansarosh UK Ltd | Professional & scientific | 2025 |
| Anthea Harrison Garden Design Limited | Administrative & support | 2014 |
| Anthony Clare Ltd | Professional & scientific | 2021 |
| Anvil House (Harpenden) Limited | Households | 1983 |
| AP Heating Services Ltd | Construction | 2025 |
| AP Properties & Homes Ltd | Real estate | 2026 |
| Apeski Limited | Information & communication | 2022 |
| Apex Assets Solutions Ltd | Real estate | 2023 |
| Apex Specialist Contracts Limited | Construction | 2017 |
| APL Plumbing Limited | Construction | 2025 |
| Apollo Nails Bishop Ltd | Other services | 2025 |
| Apower 3 - Coaching, Training & Mind Freedom Ltd | Other services | 2017 |
| Appe Pharma Consulting Limited | Professional & scientific | 2012 |
| Apple Canteen Limited | Hospitality | 2020 |
| Appleclay Limited | Administrative & support | 2017 |
| Applejack Design Services Ltd | Professional & scientific | 2020 |
| Appliance Breakdown Service Limited | Manufacturing | 1996 |
| Applied Verdict Ltd | Information & communication | 2026 |
| APS Interiors Ltd | Construction | 2015 |
| Apton Dance Studio (Essex) Limited | Arts & recreation | 2011 |
| Aquafly Business Services Ltd | Professional & scientific | 2015 |
| AR Noble Ltd | Wholesale & retail | 2021 |
| Arbor Contracts Ltd | Construction | 2023 |
| ARC Change Partners Ltd | Professional & scientific | 2018 |
| ARC Online Services Limited | Information & communication | 2022 |
| Archway Services Limited | Construction | 1987 |
| Arcoelho Digital Consulting Ltd | Information & communication | 2026 |
| Arda & Sisters Properties Ltd | Real estate | 2022 |
| Ardent HR Consulting Ltd | Professional & scientific | 2023 |
| Argb Property Ltd | Real estate | 2026 |