| Adonai Proactive Service Limited | Mining & quarrying | 2018 |
| Adorn Facilities Management Ltd | Construction | 2021 |
| Adrenalyze Leisure Ltd | Arts & recreation | 2016 |
| Adrian Trans Serv Ltd | Construction | 2010 |
| Adrianasaintee Ltd | Professional & scientific | 2025 |
| ADS Agencies Ltd | Wholesale & retail | 2017 |
| Ads-Driving Ltd | Education | 2019 |
| Adsl Services Limited | Health & social care | 2018 |
| Advance Care Consultancy Ltd | Health & social care | 2016 |
| Advance Practitioner Limited | Public administration | 2026 |
| Advanced Acoustic Installation Services Limited | Manufacturing | 2021 |
| Advanced Aerials (AV) Ltd | Construction | 2003 |
| Advanced Aesthetics Ltd | Health & social care | 2025 |
| Advanced Autoglazing Ltd | Wholesale & retail | 2014 |
| Advanced Risk Management Ltd | Professional & scientific | 2008 |
| Advanced Transport Services Ltd | Transport & logistics | 2019 |
| Advanced Turbine Services Ltd | Wholesale & retail | 2020 |
| Advancing Sustainability Ltd | Professional & scientific | 2013 |
| Advantage Business Components Ltd | Wholesale & retail | 1999 |
| Advantage Marine Services Limited | Wholesale & retail | 2017 |
| Advantage Sails Limited | Wholesale & retail | 2012 |
| Advisory 73 Limited | Professional & scientific | 2026 |
| Advocate AG Limited | Construction | 2002 |
| AE Rosario Ltd | Arts & recreation | 2023 |
| AER+ Training Limited | Education | 2025 |
| Aero Rentals Ltd | Manufacturing | 2017 |
| Aeroarb Solutions Ltd | Agriculture & fishing | 2020 |
| Aerocoat International Ltd | Professional & scientific | 2007 |
| Aerodyne Industries Limited | Professional & scientific | 2020 |
| Aerofloor Limited | Transport & logistics | 1988 |
| Aeronique Solutions Ltd | Professional & scientific | 2019 |
| Aerostat Limited | Professional & scientific | 2014 |
| AES Visual Effects Limited | Information & communication | 2023 |
| Aesrem Limited | Households | 2012 |
| Aesthetico Decorative Arts Limited | Construction | 2014 |
| Aesthetics Colchester Limited | Health & social care | 2022 |
| Aewright Limited | Professional & scientific | 2025 |
| AF Properties Essex Ltd | Real estate | 2024 |
| Afatrans Ltd | Transport & logistics | 2017 |
| Afbc CIC | Real estate | 2024 |
| AFC Pegasus Colchester Youth C.I.C. | Arts & recreation | 2021 |
| Affect Property Limited | Construction | 2024 |
| Affinia Associates Limited | Professional & scientific | 2010 |
| Affinia Group Advisory Limited | Professional & scientific | 2023 |
| Affinia Group Holdings Limited | Other services | 2019 |
| Affinia Group Services Limited | Financial services | 2024 |
| Affinia Limited | Professional & scientific | 1993 |
| Affordable Energy Limited | Construction | 2008 |
| Affordable Renewable Energy UK Limited | Construction | 2023 |
| Affordahire Limited | Administrative & support | 2026 |
| Afkan Ltd | Real estate | 2021 |
| Aflosp Property Limited | Real estate | 2025 |
| Afraid of the Dark Ltd | Extraterritorial | 2026 |
| Africa Risk Management and Compliance Partners Ltd | Professional & scientific | 2019 |
| African Aviation Alliance (AAA) Limited | Professional & scientific | 1996 |
| African Aviation Services Limited | Information & communication | 1996 |
| Afro Budgie Nest Food Limited | Wholesale & retail | 2026 |
| AFT Property Ltd | Real estate | 2022 |
| After Office Hours Colchester Ltd | Hospitality | 2008 |
| After the Rain Health & Beauty Ltd | Other services | 2016 |
| Afterglow Ltd | Hospitality | 2025 |
| Afterglow Media Ltd | Information & communication | 2016 |
| Afterglow Tanning and Beauty Ltd | Other services | 2022 |
| Afterimage Creative Limited | Professional & scientific | 2023 |
| Aftermarket Vehicle Solutions Limited | Administrative & support | 2009 |
| AG Construction CDM Services Ltd | Professional & scientific | 2025 |
| AG Detail Limited | Administrative & support | 2018 |
| AG Palapal Limited | Professional & scientific | 2011 |
| Agathiyar Limited | Information & communication | 2013 |
| AGB Services Anglia Limited | Manufacturing | 2013 |
| AGB Swimming Pools Limited | Manufacturing | 2025 |
| AGD Plastering Ltd | Construction | 2018 |
| Ages Literary Promotions Ltd | Information & communication | 2017 |
| Agile Business Coaching Limited | Professional & scientific | 2016 |
| Agile Gecko Limited | Information & communication | 2010 |
| Agile IP Holdings Limited | Professional & scientific | 2017 |
| Agile Research Limited | Information & communication | 2016 |
| Agile Software Systems Ltd | Information & communication | 2014 |
| Agility Building Consultancy Ltd | Professional & scientific | 2022 |
| AGL Steelform Ltd | Mining & quarrying | 2009 |
| AGM Surveying Ltd | Professional & scientific | 2025 |
| AGO Compliance Limited | Public administration | 2020 |
| AGO Safety Services Limited | Public administration | 2013 |
| Agonabrothers Limited | Public administration | 2025 |
| Agri-Mix Aggregates Limited | Extraterritorial | 2013 |
| Agri-Mix Limited | Wholesale & retail | 2000 |
| Agri-Mix Recycling Limited | Wholesale & retail | 2020 |
| Agricultural Car and Commercial Limited | Wholesale & retail | 2014 |
| Agrimac (UK) Limited | Wholesale & retail | 2011 |
| AGS Supplies Limited | Administrative & support | 2015 |
| Aguaconsult Ltd | Professional & scientific | 2003 |
| Aguaconsult Trustees Limited | Extraterritorial | 2023 |
| AH Bearings Ltd | Wholesale & retail | 2015 |
| AHB Transformation Limited | Professional & scientific | 2015 |
| Ahbcompany Ltd | Financial services | 2018 |
| Ahfinishings Limited | Construction | 2013 |
| AI Acquisition System Ltd | Professional & scientific | 2023 |
| AI Data Vision Ltd | Information & communication | 2023 |
| AI Generation Limited | Information & communication | 2025 |
| AI Leadership Limited | Information & communication | 2025 |