| 2-1-3 (Global)Investigations and Consultancy Ltd | Administrative & support | 2022 |
| 228 Strand Road Limited | Construction | 2021 |
| 2MC (Teesdale) Ltd. | Hospitality | 2014 |
| 55 Radnor Walk Freehold Limited | Real estate | 2014 |
| 6JD Engineering Limited | Professional & scientific | 2014 |
| 8TH House HR Ltd | Administrative & support | 2024 |
| 999 Fire and Safety Ltd | Other services | 2013 |
| A Hughes Building & Joinery Services Ltd | Construction | 2024 |
| A R C Plant Repairs Ltd | Manufacturing | 2020 |
| Abbeyfield Barnard Castle Society Limited(The) | Other services | 1967 |
| Abfab Enterprises Limited | Professional & scientific | 1996 |
| Abodoo (UK) Limited | Information & communication | 2017 |
| Absorbent Products Limited | Manufacturing | 1998 |
| Accessium Ltd | Information & communication | 2016 |
| Accounting Wyse Limited | Professional & scientific | 2025 |
| ACK Groundworks Limited | Construction | 2015 |
| Addison & Co Trustees Limited | Professional & scientific | 2026 |
| Addison Imperial Ltd | Extraterritorial | 2020 |
| Addisons Surveyors LLP | | 2010 |
| Adrian Carroll Limited | Construction | 2005 |
| ADV Bike Tours Ltd | Administrative & support | 2021 |
| Adventures in Property Limited | Real estate | 2010 |
| Adventures in Rentals Ltd | Real estate | 2022 |
| ADX Performance Ltd | Arts & recreation | 2025 |
| Af&V Launchpad Limited | Hospitality | 2013 |
| Agbr Ltd | Manufacturing | 2021 |
| AGP Assets Limited | Real estate | 2022 |
| AHV Consultants Limited | Information & communication | 2014 |
| AJM Comms Limited | Wholesale & retail | 2022 |
| Alchemy Safety Ltd | Professional & scientific | 2009 |
| Alston Road Garage & Engineering Ltd | Wholesale & retail | 2023 |
| Alternative Liqueurs Ltd | Administrative & support | 2019 |
| Altruist North East Ltd | Construction | 2021 |
| AM Quality Services Limited | Professional & scientific | 2010 |
| Andalucia (Barnard Castle) Limited | Wholesale & retail | 1999 |
| Andersons Estates & Property Limited | Real estate | 2024 |
| Andersons Paving Limited | Construction | 2016 |
| Andrew Buck Ltd | Financial services | 2008 |
| Andy Beck Images Limited | Other services | 2016 |
| Applied Design Graphics Limited | Wholesale & retail | 2019 |
| Applied Inclusive Education Systems Ltd | Education | 2025 |
| Appollo GAS Services Limited | Construction | 2007 |
| Aquilty Consulting Limited | Professional & scientific | 2018 |
| Archaeo-Environment Limited | Professional & scientific | 2003 |
| Armstrong Web Solutions Ltd | Information & communication | 2023 |
| Arrow Alignment Ltd | Manufacturing | 2011 |
| Art Impress Limited | Professional & scientific | 2013 |
| Artress (UK) Limited | Extraterritorial | 2022 |
| Artscape Co. Ltd. | Administrative & support | 2003 |
| Artsmiths Limited | Information & communication | 2013 |
| Aspire Accounting & Tax Ltd | Professional & scientific | 2018 |
| Aspire Property Rentals UK Ltd | Real estate | 2021 |
| Associated Maintenance Services Ltd | Manufacturing | 2014 |
| Athletes Foundry Ltd. | Health & social care | 2019 |
| Atkins Technology Ltd | Professional & scientific | 2025 |
| Atlas Aviation Corporation Limited | Professional & scientific | 2026 |
| Auckland Amenity Groundcare Limited | Administrative & support | 2015 |
| AWB Paving Contracts Limited | Construction | 2016 |
| Aysgarth Falls Hydro-Electric Company Limited | Energy | 2008 |
| Azonax Limited | Information & communication | 2001 |
| B-Creative NE Ltd | Information & communication | 2025 |
| B7YLS Engineering Ltd | Professional & scientific | 2018 |
| Barnard Castle CC Trading Limited | Arts & recreation | 2016 |
| Barnard Castle Christmas Lights CIC | Other services | 2018 |
| Barnard Castle Meet Limited | Arts & recreation | 2014 |
| Barnard Castle School | Education | 2008 |
| Barnard Castle Youth Football Club Limited | Arts & recreation | 2005 |
| BC Italian K Ltd | Hospitality | 2026 |
| BC Italian Ltd | Hospitality | 2024 |
| Bcgc (Services) Limited | Hospitality | 2015 |
| BE Franchising Limited | Professional & scientific | 2008 |
| Beaconsfield Management Limited | Households | 1987 |
| Beauty Therapy Clinic Limited | Wholesale & retail | 2014 |
| BEE Responsible Limited | Agriculture & fishing | 2018 |
| Belgrave House Limited | Real estate | 2018 |
| Bell Access & Engineering Ltd | Construction | 2022 |
| Bell Access (Holdings) Ltd | Agriculture & fishing | 2010 |
| Bell Ground Investigation Limited | Professional & scientific | 2019 |
| Bellmont Phase 6 Management Company Limited | Administrative & support | 2005 |
| Birch Direct Solutions Ltd | Wholesale & retail | 2024 |
| Bitville Ltd | Information & communication | 2019 |
| Blaeford Gordon & Company Limited | Professional & scientific | 2004 |
| Blaize | Arts & recreation | 1998 |
| Bleak Houses (Interiors, Homes & Decor) Limited | Real estate | 2021 |
| Block Learning Ltd | Education | 2022 |
| Bloxham Marketing Limited | Professional & scientific | 2022 |
| Bluesky Wireless Limited | Information & communication | 2006 |
| Boaz Trading Limited | Hospitality | 2023 |
| Boldron Limited | Information & communication | 2014 |
| Borfin Unlimited | Financial services | 2020 |
| Bounce a Mania Limited | Arts & recreation | 2019 |
| Briaridge Limited | Professional & scientific | 2018 |
| Briery Developments Limited | Real estate | 2024 |
| Briggs Process Services Limited | Construction | 2007 |
| Bright Woods Forest School CIC | Education | 2017 |
| Brokk Limited | Extraterritorial | 2002 |
| Business Enterprise Support & Tuition Ltd | Professional & scientific | 2003 |
| Business Services (Leicester) Limited | Professional & scientific | 2008 |
| C M F Planning and Design Ltd | Construction | 2009 |
| C.J. Tennant Engineering Limited | Construction | 2008 |