| Alan Osuoha Limited | Construction | 2013 |
| Alanda Limited | Financial services | 2009 |
| Alaro Energy Ltd | Construction | 2026 |
| Albany Associates Ltd | Real estate | 2024 |
| Albatross Pools & Spas Limited | Construction | 2007 |
| Albi and Lola Properties Ltd | Real estate | 2021 |
| Alde Fencing Limited | Administrative & support | 2013 |
| Alden Rose Ltd | Professional & scientific | 2021 |
| Alderton Services Limited | Construction | 2015 |
| Alex and Megha Limited | Health & social care | 2026 |
| Alexander Cars Limited | Wholesale & retail | 2023 |
| Alexander David Holdings Limited | Financial services | 2006 |
| Alexander Drylining Limited | Construction | 2012 |
| Alfa Construction (Essex) Limited | Construction | 2020 |
| ALH Fitness Ltd | Arts & recreation | 2023 |
| Alice Godfrey Equine Ltd | Other services | 2021 |
| Align Therapy Limited | Health & social care | 2023 |
| Align Wellbeing Limited | Health & social care | 2016 |
| Alisha Green Consultants Limited | Professional & scientific | 2014 |
| Alison Lovell Nutrition Limited | Health & social care | 2022 |
| ALL Commercial Construction Consultants Limited | Professional & scientific | 2018 |
| ALL Mortgage Care Ltd | Financial services | 2023 |
| ALL Versions of YOU Limited | Health & social care | 2024 |
| Allen TTC Ltd | Professional & scientific | 2013 |
| Allwag Holdings Limited | Financial services | 2026 |
| Allyoung Limited | Administrative & support | 2010 |
| Almeida Health Limited | Health & social care | 2024 |
| Alpha Group Commercial Ltd | Administrative & support | 2024 |
| Alpha Hive AI Limited | Information & communication | 2026 |
| Alpha K9 Security Services Ltd | Administrative & support | 2012 |
| Alpha Roofing and Building Services Limited | Construction | 2025 |
| Alpha Strategic Advisory Ltd | Professional & scientific | 2019 |
| Alpheton Garage Limited | Wholesale & retail | 2000 |
| ALT Advisors Limited | Professional & scientific | 2021 |
| Alternative USE Boston Projects (1) Limited | Energy | 2022 |
| Alternative USE Boston Projects (1)HOLDINGS Limited | Energy | 2023 |
| Alternative USE Boston Projects (Development) Limited | Energy | 2026 |
| Alternative USE Boston Projects Holdings Limited | Energy | 2023 |
| Alternative USE Limited | Energy | 2020 |
| Alternative USE Projects Limited | Energy | 2015 |
| Altior Vocatio 241 Ltd | Professional & scientific | 2023 |
| Altus Solutions Ltd | Information & communication | 2025 |
| Amarch Ltd | Professional & scientific | 2011 |
| Amaze in Taste Limited | Hospitality | 2013 |
| Amazing Grill Ltd | Hospitality | 2025 |
| Ambi Properties Ltd | Real estate | 2023 |
| Ambos Holdings Ltd | Financial services | 2024 |
| AMD Technik (Essex) Limited | Wholesale & retail | 1991 |
| Ameena ASH Ltd | Health & social care | 2023 |
| American PIE Holdings Ltd | Professional & scientific | 2002 |
| Amerigo & Co Ltd | Agriculture & fishing | 2019 |
| Amfin Consulting Ltd | Professional & scientific | 2015 |
| Amidar Consulting Ltd | Information & communication | 2016 |
| AMK Asbestos Consultancy Limited | Professional & scientific | 2013 |
| AMP Electrical Contracts Ltd | Construction | 1999 |
| AMV Property Solutions Ltd | Construction | 2025 |
| Anavad Technologies Ltd | Information & communication | 2025 |
| Andrew Cornish Ltd | Administrative & support | 2012 |
| Andrew Edmonds Enterprises Limited | Wholesale & retail | 2015 |
| Andrew M Brown Consulting Ltd | Professional & scientific | 2019 |
| Andrew Skinner Wealth Management Limited | Financial services | 2016 |
| Andrews Property Development Ltd | Real estate | 2024 |
| Andromeda Properties Ltd | Real estate | 2023 |
| Andsons Solutions Limited | Health & social care | 2021 |
| Andy Nutts Creative Imagery Ltd | Professional & scientific | 2026 |
| Angel Financial Ltd | Professional & scientific | 2015 |
| Angel Products Limited | Wholesale & retail | 2011 |
| Anglia Heating and Maintenance Engineers Limited | Construction | 2001 |
| Anglo European Services (PPE) Limited | Construction | 2002 |
| Anox Media Limited | Information & communication | 2014 |
| Anthony (Colchester) Limited | Other services | 1995 |
| Anthony Hire Limited | Wholesale & retail | 2003 |
| AP Safety Solutions Ltd | Professional & scientific | 2025 |
| Apex BIC Ltd | Construction | 2023 |
| APG Consulting Ltd | Financial services | 2022 |
| Appco Consultancy Limited | Information & communication | 2023 |
| Appcore Services Ltd | Information & communication | 2024 |
| Apple Tree Management Services Limited | Professional & scientific | 2025 |
| Approach Scaffolding Ltd | Construction | 2024 |
| Apricot Accounting Limited | Administrative & support | 2011 |
| Apricot Cloud Accounting Limited | Professional & scientific | 2017 |
| Aquagas Colchester Limited | Construction | 2023 |
| AR Advisory Services Ltd | Professional & scientific | 2024 |
| Arabic Sawa 1 Ltd | Education | 2022 |
| Araydesign Ltd | Professional & scientific | 2015 |
| Arbtek Tree Surgeons (South) Ltd | Administrative & support | 2025 |
| ARC Business Consultants Limited | Professional & scientific | 2022 |
| ARC Management Consultants Ltd | Professional & scientific | 2010 |
| Architecture - A1 Limited | Professional & scientific | 2019 |
| ARD Local Ltd | Water & waste | 2007 |
| Ardeco Interiors Limited | Construction | 2018 |
| Arebray Ltd | Real estate | 2015 |
| Arena Consultancy Services Limited | Wholesale & retail | 2013 |
| Arena Decorators Limited | Wholesale & retail | 2018 |
| Arena Surveillance Ltd | Administrative & support | 2020 |
| Argentea Limited | Financial services | 2007 |
| Argo Aviation International Limited | Other services | 2007 |
| Argyll Investments Limited | Construction | 2016 |
| Aridd Limited | Construction | 2009 |
| Aries Transport Limited | Transport & logistics | 1998 |