| Asset Accountancy Services Limited | Professional & scientific | 2002 |
| Assiduous Solutions Ltd | Professional & scientific | 2022 |
| Associate Vehicle Installations Limited | Administrative & support | 2004 |
| Associated Trainers Ltd | Education | 2002 |
| Association of Pensions & Benefits Claimants CIC | Other services | 2012 |
| Assure Personnel Ltd | Administrative & support | 2024 |
| Assure-U International Ltd | Financial services | 2019 |
| Assure-U Ltd | Financial services | 2006 |
| Assured Funding Ltd | Financial services | 2011 |
| Assured Services 1923 Ltd | Arts & recreation | 2018 |
| Astar Homecare Ltd | Health & social care | 2017 |
| Astar Pharma Limited | Professional & scientific | 2020 |
| Astell Williams Limited | Real estate | 2019 |
| Aster Suites Limited | Real estate | 2024 |
| Asterwood School Road (Management Company) Limited | Real estate | 2022 |
| Aston Core Limited | Other services | 2020 |
| Aston Lane Solar Farm Limited | Energy | 2022 |
| Astra Consulting Group Ltd | Hospitality | 2026 |
| Astra Despatch Limited | Transport & logistics | 2002 |
| Astral Forge Limited | Information & communication | 2025 |
| Astrarium Games Ltd | Information & communication | 2024 |
| Astreon Group Ltd | Wholesale & retail | 2025 |
| Astus Munia Consilium Ltd | Information & communication | 2011 |
| ASV Martlesham Limited | Wholesale & retail | 2022 |
| Asymmetric Advisors Limited | Administrative & support | 2017 |
| AT ALL Squared Limited | Professional & scientific | 2014 |
| AT Motors Essex Ltd | Wholesale & retail | 2017 |
| AT Your Doorstep Store Ltd | Wholesale & retail | 2022 |
| AT Your Home EYE Care Ltd | Health & social care | 2023 |
| AT Your Place Catering Ltd | Hospitality | 2025 |
| ATA Home Ltd | Wholesale & retail | 2023 |
| ATA Timber UK Ltd | Wholesale & retail | 2020 |
| ATB Media Limited | Arts & recreation | 2015 |
| ATE Global Ltd | Financial services | 2016 |
| Ateride Ltd | Information & communication | 2017 |
| ATH Training Group Ltd | Administrative & support | 2004 |
| Atharv Analytics Ltd | Information & communication | 2022 |
| Athena Academy Limited | Education | 2017 |
| Athena Group Services Ltd | Construction | 2020 |
| Athena HR & Training Limited | Administrative & support | 2025 |
| Athena Mechanical Services Limited | Other services | 2014 |
| Athena Recruiting Services Ltd | Administrative & support | 2014 |
| Athena Social Work Services Limited | Health & social care | 2013 |
| Atithi Stay Ltd | Hospitality | 2025 |
| ATJ Creative Limited | Professional & scientific | 2023 |
| ATK Fashion House Ltd | Other services | 2022 |
| Atkins Gregory Limited | Administrative & support | 2002 |
| Atlantic CP Holdings Limited | Real estate | 2024 |
| Atlantis Communications Limited | Information & communication | 2015 |
| Atlantis Office Limited | Wholesale & retail | 2010 |
| Atlas (UK) Limited | Professional & scientific | 1989 |
| Atlas Optical Ltd | Health & social care | 2019 |
| Atlas Print Limited | Administrative & support | 2017 |
| Atlas Tower Holdings Limited | Financial services | 2019 |
| Atom Risk Solutions Ltd | Water & waste | 2026 |
| Atom Water Holdings Limited | Financial services | 2026 |
| Atom Water Treatment Ltd | Water & waste | 2016 |
| Ator and JO Associates Ltd | Health & social care | 2019 |
| Ats(Assistance Trade Services) Ltd | Wholesale & retail | 2019 |
| Atsol Ltd | Information & communication | 2011 |
| Attachment Solutions Ltd | Manufacturing | 2010 |
| Attackedcloud TCG Limited | Wholesale & retail | 2026 |
| Attendance Solutions Essex Ltd | Education | 2015 |
| Attmere Plant Repairs Ltd | Extraterritorial | 2022 |
| ATV Solutions Ltd | Administrative & support | 2015 |
| Atva Auto Limited | Wholesale & retail | 2019 |
| Atva Homes Limited | Real estate | 2021 |
| Atva Solutions Limited | Information & communication | 2007 |
| Atz-Motion Ltd | Manufacturing | 2024 |
| AU Khan Transport Ltd | Transport & logistics | 2019 |
| Auberge Hotels Limited | Professional & scientific | 2004 |
| Auburn Online Ltd | Wholesale & retail | 2024 |
| Auction Attic Limited | Wholesale & retail | 2026 |
| Audacia Capital (UK) Limited | Administrative & support | 2022 |
| Audience Films Limited | Information & communication | 2005 |
| Audio Underground Limited | Information & communication | 2015 |
| Audio Visual Commodity Ltd | Manufacturing | 2003 |
| Audrius Gudas Ltd | Extraterritorial | 2026 |
| Aumspraxis Ltd | Professional & scientific | 2025 |
| Aunties Kitchen Ltd | Hospitality | 2024 |
| Aura & Essence Ltd | Wholesale & retail | 2025 |
| Aura Decor Studio Ltd | Other services | 2025 |
| Aura Films Ltd | Information & communication | 2013 |
| Aura Socials Limited | Professional & scientific | 2025 |
| Aurea Global Consultancy Ltd | Professional & scientific | 2025 |
| Aureon Holdings Ltd | Financial services | 2026 |
| Aureon RAY1 Ltd | Real estate | 2026 |
| Aureon RAY2 Ltd | Real estate | 2026 |
| Aurora Children's Therapy Limited | Health & social care | 2023 |
| Auston Legal Ltd | Administrative & support | 2012 |
| Autc Limited | Wholesale & retail | 2016 |
| Authentic Care Ltd | Health & social care | 2018 |
| Authentication UK Limited | Wholesale & retail | 2009 |
| Autism Anglia | Education | 1997 |
| Auto 27 Limited | Hospitality | 2022 |
| Auto AID Accident Repair Ltd | Wholesale & retail | 2005 |
| Auto Body Repairs Colchester Ltd | Wholesale & retail | 2018 |
| Auto Chrome Ltd | Wholesale & retail | 2019 |
| Auto Deals UK Ltd | Wholesale & retail | 2023 |
| Auto Select Ltd | Construction | 2020 |