| Abst Catering Ltd | Hospitality | 2026 |
| Abtek I.T. Limited | Information & communication | 1998 |
| AC Corals Ltd | Agriculture & fishing | 2022 |
| AC3 Mouldings Ltd | Construction | 2018 |
| AC3 Productions Ltd | Construction | 2018 |
| Accelerate (*a & BC) Limited | Financial services | 2020 |
| Access Health Solutions Limited | Health & social care | 2025 |
| Accountancy Professionals Limited | Real estate | 2003 |
| Accounting Services 2000 Ltd | Professional & scientific | 2009 |
| Accumulative Wealth Management Limited | Real estate | 2020 |
| Ace Signs Ltd | Manufacturing | 2024 |
| Acorn 2 Oak Property Holdings Limited | Financial services | 2026 |
| Acorn 2 Oak Support Services Ltd | Health & social care | 2022 |
| ACP Training & Development Ltd | Administrative & support | 2007 |
| ACS Aviation Industries Ltd | Transport & logistics | 2014 |
| Action Rigging Ltd | Information & communication | 2018 |
| Actiongolden Limited | Information & communication | 1996 |
| Actis Skillset Limited | Professional & scientific | 2003 |
| Activate Holdings Ltd | Financial services | 2023 |
| Activate Lubricants Limited | Wholesale & retail | 2015 |
| Active GAS & Heating Services Ltd | Construction | 2017 |
| Ad-Tek Finishings Limited | Manufacturing | 2003 |
| Ad-Tek Products Limited | Manufacturing | 2000 |
| Adam & YAZ Ltd | Wholesale & retail | 2022 |
| Adam Patrickson (A&P) Ltd | Real estate | 2024 |
| Adas.Design Ltd | Manufacturing | 2025 |
| Adas.Social Ltd | Information & communication | 2025 |
| ADC Productions Ltd | Construction | 2021 |
| ADG Locum Services Ltd | Other services | 2023 |
| ADH Porsche Ltd | Wholesale & retail | 2018 |
| ADS Publishing Ltd | Information & communication | 2024 |
| Advanced Electricity Networks Limited | Energy | 2023 |
| Advanced Performance AI Ltd | Professional & scientific | 2026 |
| Advanced Utility Asset Networks Limited | Financial services | 2023 |
| Advanced Utility Networks Limited | Financial services | 2022 |
| Advanced Water Infrastructure Networks Limited | Water & waste | 2023 |
| Aegros Health PCN Limited | Health & social care | 2024 |
| AER Maven Limited | Manufacturing | 2012 |
| Aerocraft Beverages Limited | Manufacturing | 2020 |
| Aerocraft Hospitality Limited | Manufacturing | 2025 |
| Aetherial Ltd | Information & communication | 2023 |
| Aethersys Limited | Information & communication | 2007 |
| Afdent Limited | Health & social care | 2004 |
| Affinity Cleaning Services Limited | Administrative & support | 2019 |
| AFP Transport Limited | Transport & logistics | 2001 |
| African Supplier Group Ltd | Health & social care | 2022 |
| AGH Property Solutions Ltd | Real estate | 2024 |
| Agile Regulatory Limited | Public administration | 2021 |
| AGR Solutions Ltd | Construction | 2024 |
| AHM Plumbing & Heating Limited | Construction | 2021 |
| Aidcall Limited | Wholesale & retail | 1998 |
| Aina Homes Ltd | Real estate | 2019 |
| AIP Closing Ltd | Information & communication | 2014 |
| Air 2 Limited | Construction | 2025 |
| Air Results Ltd | Professional & scientific | 2024 |
| Aira Capital Ltd | Real estate | 2020 |
| Airburner UK Limited | Agriculture & fishing | 2007 |
| Airline Component Services Limited | Transport & logistics | 2005 |
| AIT Medihelp Limited | Education | 2009 |
| AJ Essex Ltd | Construction | 2022 |
| AJ FM Ltd | Administrative & support | 2025 |
| Aj's Culinary Creations Limited | Hospitality | 2024 |
| AJB Property Consultants Ltd | Administrative & support | 2017 |
| AJH Porsche Specialists Limited | Wholesale & retail | 2025 |
| AJN London Limited | Health & social care | 2022 |
| Akshnee Limited | Real estate | 2015 |
| Al-Falah Braintree Islamic Centre Ltd. | Other services | 2001 |
| Albeenuta Ltd | Wholesale & retail | 2021 |
| Alcedin Consulting Ltd | Professional & scientific | 2024 |
| Alchemy Global Talent Solutions Ltd | Administrative & support | 1995 |
| Aldridge's Property Services Ltd | Construction | 2023 |
| Alec Hunter PRE School | Education | 2010 |
| Alethia Pneuma Asset Management Limited | Real estate | 2025 |
| Alex MAY Studio Ltd | Professional & scientific | 2017 |
| Alexander Mandeville Construction Limited | Public administration | 2014 |
| Aleys Yard Management Company Limited | Households | 2019 |
| Alfacon Services Ltd | Construction | 2026 |
| Alfamail Publishers Limited | Information & communication | 2018 |
| Aligned Studios Ltd | Professional & scientific | 2021 |
| ALL 4 Logistics Ltd | Transport & logistics | 2017 |
| ALL Around Cleaning Company Limited | Administrative & support | 2015 |
| ALL Car Cabs Ltd | Transport & logistics | 2024 |
| ALL Colour Windows and Doors Limited | Professional & scientific | 2014 |
| ALL Over Security Ltd | Administrative & support | 2021 |
| ALL Seasons Tipis Ltd | Administrative & support | 2019 |
| ALL Spice Braintree Limited | Hospitality | 2025 |
| ALL Systems to Grow Limited | Wholesale & retail | 2019 |
| All-Clear Skip Hire Limited | Administrative & support | 2005 |
| Alla Domestics Ltd | Households | 2003 |
| Allamber Ltd | Hospitality | 2009 |
| Allegro Music Limited | Wholesale & retail | 1989 |
| Alliance of Bioenergetic Consultants Limited | Health & social care | 2012 |
| Alliance Sports Innovation Limited | Wholesale & retail | 2017 |
| Alloy Logic Ltd | Wholesale & retail | 2014 |
| Alluminate Ltd | Information & communication | 2025 |
| Alma Tron Limited | Construction | 2003 |
| Almir Properties Ltd | Real estate | 2025 |
| Alpha-Networks.Net Limited | Information & communication | 2003 |
| Alphatemp Technology Limited | Manufacturing | 2006 |
| Alta Vista Consulting Limited | Professional & scientific | 2019 |