| Arora Fitness Limited | Wholesale & retail | 2019 |
| Aroy Thai Cafe Ltd | Hospitality | 2023 |
| Arrow Electrical Distributors Ltd | Administrative & support | 2000 |
| Artech Lighting (Caledonia) Limited | Manufacturing | 2021 |
| Artech Lighting (London) Limited | Manufacturing | 2021 |
| Arthos Trade Ltd | Wholesale & retail | 2025 |
| Artisan (2018) Limited | Manufacturing | 2018 |
| Artisan CAD Limited | Professional & scientific | 2016 |
| Artisan Dawn Ltd | Manufacturing | 2023 |
| AS GAS Services Ltd | Construction | 2017 |
| Asas Store Ltd | Wholesale & retail | 2025 |
| Ascension Physiotherapy Limited | Health & social care | 2020 |
| ASD Property Projects Ltd | Construction | 2025 |
| ASH Coffee Group Limited | Wholesale & retail | 2024 |
| Ashby-Scott Projects Limited | Professional & scientific | 1997 |
| Ashcroft Jewellery Design Ltd | Wholesale & retail | 2018 |
| Ashdown Architects Limited | Professional & scientific | 2002 |
| Ashes of Love Ltd | Extraterritorial | 2026 |
| Ashford & Carter Investments Ltd | Financial services | 2025 |
| Ashmere Projects Ltd | Construction | 2026 |
| Asia Group Holdings Ltd | Financial services | 2025 |
| Asia Group Real Estate Ltd | Financial services | 2025 |
| Aspen Consult Management Systems Ltd | Professional & scientific | 2025 |
| Asphereal Ltd | Transport & logistics | 2023 |
| Aspire Roofing and Maintenance Ltd | Construction | 2023 |
| Asre Global Limited | Real estate | 2022 |
| Asset Appointments Ltd | Administrative & support | 2007 |
| Asset Class Investments UK Limited | Real estate | 2017 |
| Asset Rank Investments Ltd | Real estate | 2025 |
| Assist Accounts & Payroll Ltd | Professional & scientific | 2013 |
| Associated Property Investors Limited | Real estate | 2004 |
| Associates Hair, Body and Mind Limited | Other services | 2012 |
| Assure Collective Ltd | Administrative & support | 2024 |
| Astekcomlake Ltd | Wholesale & retail | 2025 |
| Aston Knight Ltd | Construction | 2022 |
| Astral Inspections Ltd | Information & communication | 2023 |
| Asylum Hair and Beauty Ltd | Other services | 2018 |
| AT Home Mortgages Limited | Financial services | 2014 |
| AT Management Consultancy Limited | Financial services | 2020 |
| Atelier DE Potamus Limited | Wholesale & retail | 2024 |
| ATI Property North East Ltd | Real estate | 2025 |
| Atkinson Land Management Services Limited | Real estate | 2025 |
| Atkinsons (NE) Limited | Construction | 2023 |
| Atkinsons Building Services Ltd | Construction | 2024 |
| Atkinsons Lettings Limited | Real estate | 2026 |
| Atlanta Couriers Limited | Transport & logistics | 2012 |
| Atorus Consult (Durham) Limited | Information & communication | 2012 |
| Atorus Consult Limited | Information & communication | 2015 |
| Atterbury Consultancy Limited | Administrative & support | 2017 |
| AUA Investment Limited | Professional & scientific | 2026 |
| Auckland Home Solutions CIC | Hospitality | 2010 |
| Audemic Ltd | Information & communication | 2022 |
| Audiology Screening Limited | Health & social care | 2011 |
| Aukestra CIC | Education | 2015 |
| Auld Management Solutions Ltd | Administrative & support | 2015 |
| Aura Optima Limited | Arts & recreation | 2024 |
| Auratem Ltd | Wholesale & retail | 2025 |
| Aurius International Ltd | Transport & logistics | 2023 |
| Auroco UK Limited | Professional & scientific | 2024 |
| Aurora Edventures Ltd | Education | 2025 |
| Autofusion North East Ltd | Administrative & support | 2022 |
| Autoglass Assist Limited | Wholesale & retail | 2017 |
| Automated Accounting Ltd | Professional & scientific | 2019 |
| Auton Hair Clinic Limited | Other services | 2019 |
| Auton Style Ltd | Other services | 2015 |
| Autoparkuk Limited | Wholesale & retail | 2018 |
| Autorepairuk Ltd | Wholesale & retail | 2019 |
| Avenue 6 Limited | Information & communication | 2019 |
| AW Consultancy (NE) Limited | Health & social care | 2024 |
| AW Groundwork Solutions Ltd | Construction | 2023 |
| Awaken Learning Ltd | Information & communication | 2009 |
| Awareness Plus Ltd | Education | 2025 |
| Awesome Giftware Ltd | Wholesale & retail | 2013 |
| Awesome Since 84 Ltd | Arts & recreation | 2017 |
| AWM Groundworks Ltd | Construction | 2024 |
| AWR Office Limited | Manufacturing | 2025 |
| Axetera Limited | Information & communication | 2010 |
| Axil Limited | Information & communication | 2008 |
| Axiopharm Limited | Wholesale & retail | 2011 |
| Axis Test Laboratories Ltd | Professional & scientific | 2010 |
| Aybey Ltd | Wholesale & retail | 2025 |
| Aycliffe Car Valeting Srvice Ltd | Administrative & support | 2025 |
| Aycliffe Developments Limited | Real estate | 2019 |
| Aykley Construction Darras Hall Ltd | Construction | 2025 |
| Aykley Construction Ltd | Construction | 2022 |
| Aykley Group Ltd | Financial services | 2025 |
| Aykley Handyman Services Durham Ltd | Real estate | 2023 |
| Aykley Heads Business Centre Tenants' Association Limited | Real estate | 1994 |
| Ayling Hospitality Group Limited | Hospitality | 2025 |
| Ayman Hospitality Ltd | Hospitality | 2022 |
| Azgedessa Ltd | Wholesale & retail | 2025 |
| Azra Kemal Properties and Investment Ltd | Real estate | 2023 |
| Aztec North Limited | Real estate | 2015 |
| Azul Services Ltd | Construction | 2015 |
| B & S Project Management Services Ltd | Administrative & support | 2005 |
| B & W Bricklayers Ltd | Construction | 2020 |
| B Ferris Construction NE Ltd | Construction | 2021 |
| B&C (Haulage) Limited | Transport & logistics | 2025 |
| B&H Groudworks Ltd | Construction | 2020 |
| B-Print, Display & Logistics Limited | Manufacturing | 2026 |