| A-List Villas Limited | Households | 2016 |
| A. Allisters Limited | Construction | 2023 |
| A. P. Chapman Decorators Limited | Construction | 2005 |
| A.C.L. Electrical Limited | Construction | 1967 |
| A.E. Distribution Limited | Wholesale & retail | 1995 |
| A.E.Simmons Limited | Manufacturing | 1946 |
| A.F. Original Limited | Manufacturing | 2019 |
| A.G. Engineering Welding & Fabrication Services Limited | Manufacturing | 2014 |
| A.G.A.I. & Co Limited | Real estate | 2010 |
| A.H. Wright Consulting Limited | Hospitality | 2016 |
| A.H.Nicholls & Sons Limited | Water & waste | 1956 |
| A.J. Communications Limited | Information & communication | 1998 |
| A.J.W. Diving Limited | Professional & scientific | 2015 |
| A.Johnson Inc Ltd | Construction | 2025 |
| A.K. Woricker & Sons Limited | Construction | 1987 |
| A.P.M Building Ltd | Construction | 2020 |
| A.P.S. Plant Services Limited | Construction | 1991 |
| A.R. Property Designs Ltd | Professional & scientific | 2017 |
| A.T. Collings Limited | Agriculture & fishing | 2014 |
| A.T.B. Plastics Limited | Manufacturing | 1987 |
| A.W. & G.W. Day Limited | Agriculture & fishing | 1976 |
| A1 Burger Van Ltd | Hospitality | 2025 |
| A1 Care Group Limited | Health & social care | 2019 |
| A1 Dynasty Ltd | Wholesale & retail | 2017 |
| A1 Home Care Ltd | Real estate | 2007 |
| A1 Safes Limited | Administrative & support | 2006 |
| A1 Sports Group Ltd | Wholesale & retail | 2019 |
| A1 Transporter Ltd | Transport & logistics | 2022 |
| A3M Technologies Ltd. | Information & communication | 2016 |
| A82 Group Ltd | Financial services | 2016 |
| AA Advisors Europe Limited | Financial services | 2011 |
| AA Legacy Ltd | Real estate | 2026 |
| Aa&G Investments Ltd | Real estate | 2022 |
| Aa&G Management Consulting Ltd | Professional & scientific | 2014 |
| AAA Pension Limited | Professional & scientific | 2026 |
| Aaghna Ltd | Health & social care | 2024 |
| Aajet Ltd | Health & social care | 2026 |
| Aaltg Ltd | Hospitality | 2025 |
| Aaron Desmond Consulting Limited | Professional & scientific | 2014 |
| Aaron Thomas Consulting Ltd | Professional & scientific | 2025 |
| Aaronite Partners Limited | Extraterritorial | 2011 |
| Aarshya Accountancy Services Limited | Professional & scientific | 2019 |
| Aarya Homes Limited | Real estate | 2020 |
| AB - Zero AC Ltd | Construction | 2016 |
| AB Electrical Essex Ltd. | Construction | 2018 |
| AB Global Trades Ltd | Wholesale & retail | 2026 |
| AB Hand Car Wash Ltd | Administrative & support | 2023 |
| AB World Trades Ltd | Wholesale & retail | 2026 |
| Ab-Factor Training & Consulting Limited | Information & communication | 2024 |
| Abacus Aluminium Limited | Construction | 2018 |
| Abacus Mechanical & Electrical Ltd | Professional & scientific | 2020 |
| Abacus Windows and Doors Ltd | Professional & scientific | 2001 |
| Abacus Windows Commercial Limited | Manufacturing | 1998 |
| Abakare Dynamics Limited | Transport & logistics | 2024 |
| Abana Catering Services Limited | Hospitality | 2023 |
| Abba Motorcycle Equipment UK Ltd | Manufacturing | 2015 |
| Abbey Building Contractors Ltd | Construction | 2016 |
| Abbey Services Limited | Construction | 2022 |
| Abbey Walk Coggeshall Management Co Ltd | Households | 2025 |
| Abbie King Limited | Professional & scientific | 2016 |
| Abbotsleigh Maintenance North Limited | Households | 1979 |
| Abbotsleigh Maintenance South Limited | Households | 1979 |
| Abbotts Build Hub Ltd | Construction | 2025 |
| Abbotts Green (Woolpit) Management Company Limited | Households | 2021 |
| Abby Zihler Ltd | Professional & scientific | 2024 |
| ABC Aesthetics Ltd | Other services | 2022 |
| ABC Build Limited | Construction | 2018 |
| Abcor FX Limited | Financial services | 2021 |
| ABE Welding Services Limited | Manufacturing | 2015 |
| Aberthaw Energy (Holdings) Limited | Financial services | 2022 |
| Aberthaw Energy Limited | Construction | 2021 |
| Abide Services Ltd | Real estate | 2020 |
| Ability Therapies Limited | Health & social care | 2020 |
| Abington Court RTM Company Limited | Households | 2004 |
| Able Life Limited | Real estate | 2001 |
| Ablin Consult Ltd | Real estate | 2022 |
| ABM IT Ltd | Information & communication | 2026 |
| ABM Roofing Ltd | Construction | 2018 |
| Above & Beyond Management Limited | Administrative & support | 2016 |
| Above 100 Events Ltd | Arts & recreation | 2020 |
| Above Difference Limited | Professional & scientific | 2017 |
| Aboveaero Ltd | Administrative & support | 2025 |
| Abraxas Consulting LLP | | 2015 |
| ABS Group (UK) Limited | Construction | 1990 |
| Absa Properties Ltd | Real estate | 2023 |
| Absha Fashion Studio Ltd | Wholesale & retail | 2025 |
| Absl Holdings Limited | Extraterritorial | 2014 |
| ABSL1 Limited | Real estate | 2014 |
| Absolut Property Services Ltd | Real estate | 2006 |
| ABT Advisory Limited | Professional & scientific | 2014 |
| ABT Property Ltd | Real estate | 2021 |
| Abundat Holdings Limited | Financial services | 2020 |
| AC Civils Ltd | Construction | 2026 |
| AC Electrical (Chelmsford) Ltd | Construction | 2026 |
| AC Electrical Consulting Services Limited | Energy | 2017 |
| AC Event Promotions Ltd | Arts & recreation | 2026 |
| AC Integrated Solutions Limited | Construction | 2024 |
| AC Maxim Limited | Construction | 2008 |
| Acacia Advisory Ltd | Professional & scientific | 2025 |
| Acacia Conservatories Limited | Construction | 2005 |