| Acrol Air Conditioning Co. Limited | Administrative & support | 1976 |
| Acrol Modular Buildings Ltd | Construction | 1997 |
| ACS Consultancy Services Ltd | Professional & scientific | 2024 |
| Acting UP Productions LLP | | 2021 |
| Action Dynamics Limited | Arts & recreation | 2021 |
| Activaeon Limited | Information & communication | 2004 |
| Active Pictures (Film & Television) Limited | Information & communication | 1999 |
| Active Plumbing Solutions Limited | Construction | 2016 |
| Adam & IAN Mcdonald Services Limited | Water & waste | 1999 |
| Adams Barberz Ltd | Other services | 2024 |
| Adapt 2 Change Limited | Construction | 2025 |
| Adar Holdings Ltd | Financial services | 2021 |
| Addison Lambert Ltd | Extraterritorial | 2015 |
| Addison MOT Centre Limited | Manufacturing | 2017 |
| Addoque Marine Consultants Ltd | Transport & logistics | 2022 |
| Adeam Pathology Ltd | Health & social care | 2021 |
| Adelino Araujo Logistics Limited | Transport & logistics | 2025 |
| ADI Courier Ltd | Wholesale & retail | 2020 |
| Adil Mukhtar Ltd | Professional & scientific | 2025 |
| Adinu Ltd | Health & social care | 2013 |
| Adivelop Ltd | Real estate | 2021 |
| Adjoint Ltd | Information & communication | 2025 |
| Adlink Edge Computing Limited | Wholesale & retail | 2021 |
| ADM Automation Limited | Manufacturing | 1979 |
| Admin Support Specialist Limited | Administrative & support | 2022 |
| ADN Properties North East Limited | Real estate | 2021 |
| Adrian Dodds Joinery and Construction Ltd | Construction | 2019 |
| ADS Premier Projects Limited | Professional & scientific | 2024 |
| Advance Software Limited | Professional & scientific | 2000 |
| Advanced Academics Hub Ltd | Education | 2023 |
| Advanced Aesthetics Academy and Wellness Centre Ltd | Education | 2024 |
| Advanced Application Solutions Ltd | Manufacturing | 2024 |
| Advanced Bladetech Ltd | Manufacturing | 2020 |
| Advantage Utilities Services Limited | Manufacturing | 2006 |
| Advantex Network Solutions Limited | Information & communication | 2002 |
| Advantix Consulting Ltd | Professional & scientific | 2025 |
| ADVERTISE1 Ltd | Professional & scientific | 2020 |
| Advocate Education LLP | | 2011 |
| Advocate Recruitment Ltd | Administrative & support | 2015 |
| Adélie Studios Limited | Other services | 2023 |
| Aegean EYE Spirit Company Ltd. | Manufacturing | 2019 |
| Aegis Intelligence Ltd | Information & communication | 2025 |
| AER Electric Company Limited | Manufacturing | 2017 |
| Aero Inspect Limited | Professional & scientific | 2025 |
| Aerochis Limited | Professional & scientific | 2010 |
| Aerospa Beauty Ltd | Wholesale & retail | 2012 |
| Aerospa Lounge Limited | Wholesale & retail | 2018 |
| Aerospa Relaxation Limited | Wholesale & retail | 2013 |
| Aerospa Salon Ltd. | Wholesale & retail | 2014 |
| Aerotech Aviation Services Ltd | Manufacturing | 2026 |
| Aesthetic Response Ltd | Administrative & support | 2011 |
| Aesthetichem Ltd | Wholesale & retail | 2023 |
| Aevec Ltd | Professional & scientific | 2025 |
| AFD Freight Ltd | Transport & logistics | 2023 |
| Affinity Business Partners Limited | Professional & scientific | 2011 |
| Affinity Media NE CIC | Information & communication | 2019 |
| Affinity Systems Limited | Wholesale & retail | 2010 |
| Affordable Business Solutions Ltd | Financial services | 2022 |
| Affordable Homes 4U Ltd | Real estate | 2022 |
| Affordable Waste Management Ltd | Water & waste | 2020 |
| Afiaa Limited | Health & social care | 2025 |
| AFM Global Limited | Wholesale & retail | 2026 |
| Afribuild Global Sourcing Ltd | Wholesale & retail | 2025 |
| After the Jabs Ltd | Real estate | 2024 |
| AFY Aesthetics Limited | Other services | 2024 |
| AG & LE Limited | Health & social care | 2022 |
| Agaland Fashion London Ltd | Wholesale & retail | 2023 |
| Agamm Ltd | Construction | 2025 |
| AGE UK Gateshead Limited | Health & social care | 1984 |
| Ager Estates Limited | Real estate | 2024 |
| Agile Marketing Consultancy Limited | Professional & scientific | 2017 |
| Agile Property Maintenance Limited | Construction | 2023 |
| Agno Properties Limited | Real estate | 2025 |
| AGU Works Ltd | Construction | 2026 |
| AH Metal & Waste Recycling Ltd | Manufacturing | 2025 |
| Ahead of the Grain Limited | Other services | 2020 |
| Ahmad Holdings Limited | Real estate | 2020 |
| Ahmed's Grill Ltd | Hospitality | 2026 |
| AIE Fixings Limited | Wholesale & retail | 2016 |
| AIM to Recycle Limited | Financial services | 2001 |
| Air Conditioning & Refrigeration Compressors UK Limited | Administrative & support | 2020 |
| Air Design Systems (Holdings) Limited | Financial services | 2018 |
| Air Design Systems Limited | Construction | 1993 |
| Air Purification Skroll Limited | Professional & scientific | 2017 |
| Airowlite Limited | Manufacturing | 2012 |
| Airowsafe Limited | Information & communication | 2010 |
| Airowtech Electrical Distributors Limited | Wholesale & retail | 2009 |
| Airport Cars Durham Ltd | Transport & logistics | 2024 |
| AJ Manufacturing and Maintenance Ltd | Construction | 2019 |
| AJ Online Ltd | Wholesale & retail | 2016 |
| AJ Properties (North East) Limited | Real estate | 2017 |
| AJD Property Management Limited | Professional & scientific | 2026 |
| AJE Clothing Ltd | Wholesale & retail | 2017 |
| AJE Interiors (NE) Limited | Wholesale & retail | 2022 |
| Ajkal Ltd | Hospitality | 2026 |
| AJP Property Services (NE) Ltd | Real estate | 2019 |
| Ajpub Enterprise Company Limited | Hospitality | 2025 |
| AJR Medical Consultancy Limited | Health & social care | 2019 |
| AK Comfort Ltd | Real estate | 2026 |
| AK Medical Services NE Ltd | Real estate | 2014 |