| A. J. Clacher Limited | Construction | 1979 |
| A. Parker Plumbing Limited | Construction | 2009 |
| A.B. Makepeace Limited | Wholesale & retail | 1977 |
| A.Carlyle & Co. Limited | Real estate | 1988 |
| A.E. Burt and Company Limited | Real estate | 1977 |
| A.K Medical Consultancy Ltd | Wholesale & retail | 2011 |
| A.R.B Estates Ltd | Real estate | 2021 |
| A.S.Crocker(Plasterers)Limited | Construction | 1956 |
| A1 Autoscreen NE Ltd | Wholesale & retail | 2017 |
| A1 Building & Maintenance Ltd | Administrative & support | 2020 |
| A1 Home and Gardens Ltd | Water & waste | 2018 |
| A1 Motorcycle Training School Ltd | Other services | 2011 |
| A1 Paving & Landscaping Limited | Administrative & support | 2019 |
| A1 Rubbish Removal Ltd | Water & waste | 2015 |
| A1 Tyres NE Ltd | Wholesale & retail | 2025 |
| A1-TYRES Northeast Ltd | Wholesale & retail | 2017 |
| A1M Locksmiths Limited | Administrative & support | 2016 |
| A2B Transport Group Ltd | Transport & logistics | 2019 |
| A3 Homes LLP | | 2021 |
| A3 Homes UK Limited | Real estate | 2026 |
| A66 MH Limited | Hospitality | 2019 |
| AAA Car Sale Ltd | Wholesale & retail | 2019 |
| AAA Homecare Limited | Health & social care | 2023 |
| AAA Properties (NE) Ltd | Real estate | 2023 |
| Aablar Limited | Information & communication | 2022 |
| Aansquare Ltd | Wholesale & retail | 2026 |
| Aartha Properties Ltd | Real estate | 2024 |
| AB Rent a Home Ltd | Real estate | 2025 |
| ABA Locums Limited | Health & social care | 2010 |
| Abbas Leencoo Logistics Ltd | Transport & logistics | 2025 |
| Abbey Estates (North East) Limited | Extraterritorial | 2015 |
| Abbeyfield (Darlington) Society Limited (the) | Health & social care | 1970 |
| Abbie’S World Limited | Administrative & support | 2025 |
| Abbots Barton Limited | Real estate | 2025 |
| ABC Agency NE Limited | Other services | 2025 |
| ABC Roofing (North East) Ltd | Construction | 2017 |
| Abdulkarim Hnawi General Trading Ltd | Wholesale & retail | 2025 |
| Abegorge Limited | Professional & scientific | 2017 |
| Abeksgold Limited | Wholesale & retail | 2025 |
| Abel Solutions (Northern) Ltd | Administrative & support | 2012 |
| ABL Decking Ltd | Administrative & support | 2022 |
| ABL Estates NE Ltd | Real estate | 2024 |
| ABS Pumps UK Ltd | Wholesale & retail | 2019 |
| Absass Limited | Construction | 2018 |
| Absolutely Floor Restore Ltd | Construction | 2023 |
| Abu's Restaurant Ltd | Hospitality | 2025 |
| AC Power Systems Limited | Construction | 2008 |
| ACCOUNT3 Ltd. | Education | 1991 |
| Accounted 4 Limited | Professional & scientific | 2009 |
| Accounting for Your Success Ltd | Professional & scientific | 2023 |
| Accounts Agency Limited | Professional & scientific | 2014 |
| Accounts for Flooring Limited | Professional & scientific | 2025 |
| Accurate Systems Labelling Limited | Manufacturing | 2010 |
| Ace Joinery and Property Maintenance Ltd | Construction | 2022 |
| Ace Plasterers Darlington Ltd | Construction | 2022 |
| Ace Plasterers Ltd | Construction | 2010 |
| Acehawk Aerospace Ltd | Professional & scientific | 2021 |
| Achieving Change Limited | Professional & scientific | 2018 |
| Acklam Cladding Ltd | Construction | 2025 |
| ACL Document Services Ltd | Administrative & support | 2023 |
| Acme Traders Limited | Wholesale & retail | 2025 |
| Acnz 2022 Ltd | Construction | 2022 |
| Acorn Care (NE) Ltd | Health & social care | 2010 |
| Acorn Care (UK) Limited | Health & social care | 2008 |
| Acorn Dairy Limited | Wholesale & retail | 2009 |
| Acorn Fabrications Ltd | Manufacturing | 2016 |
| Acorn Properties (Jesmond) Limited | Real estate | 2000 |
| Acumen Investment & Pension Solutions Ltd | Financial services | 2020 |
| Acute Pest Solutions Ltd | Administrative & support | 2015 |
| AD Silva PVT Ltd | Hospitality | 2024 |
| Adam Grant Homes Ltd | Real estate | 2022 |
| Adam Parker Property Ltd | Households | 2015 |
| Adams Pizzeria Darlington Ltd | Hospitality | 2018 |
| Adams Property Yorkshire Ltd | Real estate | 2022 |
| Adaptive Health and Safety Limited | Extraterritorial | 2021 |
| Adaptive HR Limited | Extraterritorial | 2021 |
| Adddg Ltd | Professional & scientific | 2023 |
| Addisco Limited | Health & social care | 2013 |
| Addison Langstone Ltd | Construction | 2026 |
| Addsovem Ltd | Wholesale & retail | 2025 |
| Adebio Properties Limited | Real estate | 2024 |
| Adeniran Limited | Wholesale & retail | 2018 |
| Adept Services Limited | Administrative & support | 2007 |
| ADG Architects Limited | Professional & scientific | 2013 |
| Adlam Financial Limited | Financial services | 2015 |
| Admin Helpers Limited | Administrative & support | 2008 |
| Administration Evaluation Services Ltd | Professional & scientific | 2025 |
| Adora Properties Ltd | Real estate | 2019 |
| Adoro Caffe Limited | Hospitality | 2019 |
| ADR Electrical Services Ltd | Professional & scientific | 2020 |
| Adrian Hunter Ltd | Information & communication | 2019 |
| Adrian.Calistru Ltd | Transport & logistics | 2022 |
| Advance Business Consultancy Limited | Administrative & support | 2015 |
| Advance Rooflines Limited | Construction | 2025 |
| Advanced Fibres Ltd | Manufacturing | 2026 |
| Advanced Garage and MOT Center Limited | Wholesale & retail | 2017 |
| Advanced Inspections Limited | Construction | 2016 |
| Advanced Mortgage Solutions North East Limited | Financial services | 2021 |
| Advantagesignz Limited | Professional & scientific | 2010 |
| Advantia Solutions Ltd | Professional & scientific | 2025 |