| Brushstroke Murals Ltd | Arts & recreation | 2025 |
| Bsjm Investments Ltd | Real estate | 2026 |
| BSS Plumbing and Heating Limited | Construction | 2023 |
| Buffalo Haulage Ltd | Transport & logistics | 2025 |
| Bumblebee Computers Limited | Information & communication | 2019 |
| Butterfly Bouquets Ltd | Wholesale & retail | 2021 |
| Bvds Developments Limited | Construction | 2016 |
| BWS Retail Limited | Wholesale & retail | 2023 |
| Byre & Hayloft Ltd | Real estate | 2025 |
| C & D Remedials Ltd | Other services | 2023 |
| C & D Window Repair Limited | Construction | 2022 |
| C Carr Property & Investments Ltd | Real estate | 2025 |
| C Coxon Ltd | Transport & logistics | 2026 |
| C&K Logistics Limited | Transport & logistics | 2020 |
| C. & A.J. Anderson Foods Ltd | Hospitality | 2008 |
| C.R Cable Installations Ltd | Construction | 2022 |
| C.T.H. Installations Limited | Construction | 2022 |
| Caballus Equine Services Limited | Agriculture & fishing | 2021 |
| Cairo Luxora Ltd | Professional & scientific | 2024 |
| Capidar Limited | Construction | 2016 |
| Capiren Limited | Real estate | 2016 |
| Car Care Peterlee Ltd | Wholesale & retail | 2022 |
| Car Clinic Peterlee Limited | Wholesale & retail | 2015 |
| Carrs Recovery Limited | Wholesale & retail | 2025 |
| Cassop Consultants LLP | | 2019 |
| Castle Dene Housing Limited | Real estate | 2003 |
| Castle Dene Surgery Limited | Health & social care | 2006 |
| Castle Eden Lift Trucks Limited | Manufacturing | 2012 |
| Castlegate Landscaping Limited | Administrative & support | 2024 |
| Catering Equipment Fabrications Limited | | 1985 |
| CCTV2U Ltd | Professional & scientific | 2023 |
| CDI Energy Ltd | Construction | 2018 |
| Cece Rowe Properties Limited | Real estate | 2024 |
| CGW Contracting Ltd | Information & communication | 2022 |
| Chaganti Limited | Wholesale & retail | 2022 |
| Charlotte Dove's Safety Solutions Limited | Public administration | 2025 |
| Charlton Blair Limited | Real estate | 2012 |
| Charltons Food Limited | Hospitality | 2018 |
| Chilla Pizza & Valentinos Ltd | Hospitality | 2026 |
| Chilli Pepper Takeaway Ltd | Hospitality | 2023 |
| Chilli Pizza Limited | Hospitality | 2026 |
| Church Street Gold Limited | Wholesale & retail | 2002 |
| Cimthog Limited | Health & social care | 2022 |
| Cj's Executive Travel Limited | Transport & logistics | 2020 |
| Cj's Property Management Limited | Real estate | 2026 |
| CKM Transport Haulage Contractors Ltd | Transport & logistics | 2021 |
| Clarkson Invest Ltd | Real estate | 2022 |
| CLD Inspection Ltd | Professional & scientific | 2025 |
| Climbnrig Ltd | Construction | 2024 |
| CM AI Ltd | Construction | 2025 |
| CMS (UK) Limited | Wholesale & retail | 2012 |
| Coatman Park Leisure Limited | Hospitality | 2025 |
| Coconut Travel Limited | Administrative & support | 2021 |
| Cole's Camo Ltd | Wholesale & retail | 2024 |
| Complete Spray Services Limited | Manufacturing | 2019 |
| Connect Data and Telecoms Limited | Administrative & support | 2022 |
| Connect GAS and Power Limited | Administrative & support | 2022 |
| Conservatory Warm Roofs Limited | Households | 2017 |
| Corefusion Development Ltd | Construction | 2025 |
| Corkhill EVE Limited | Construction | 2011 |
| County Durham Security Ltd | Administrative & support | 2019 |
| Cozee Warm Limited | Wholesale & retail | 2015 |
| CR Hotham Engineering Ltd | Professional & scientific | 2021 |
| Creative Youth Opportunities CIC | Arts & recreation | 2014 |
| CRL Removals Limited | Transport & logistics | 2017 |
| Crosbys Catering Supplies Ltd. | Wholesale & retail | 2017 |
| Crossgate Durham Limited | Health & social care | 2024 |
| CRW Roadworks Ltd | Construction | 2025 |
| CTA Eurotherm Limited | | 1991 |
| CTB Jointing Services Ltd | Construction | 2023 |
| D&S - Dawid & Sons Transport Ltd | Transport & logistics | 2023 |
| Daniel W Limited | Real estate | 2014 |
| Dave Scott North East Ltd | Construction | 2019 |
| David Charles Actuarial Contracting and Enterprises Limited | Information & communication | 2007 |
| David Ward Construction Ltd | Construction | 2025 |
| Davis Terrace Convenience Store Ltd | Wholesale & retail | 2023 |
| Daytrans Limited | Transport & logistics | 2012 |
| DB Associates (Surveyors) Limited | Professional & scientific | 2010 |
| DC Private Hire Ltd | Transport & logistics | 2025 |
| Decorative Doorways Limited | Wholesale & retail | 2002 |
| Decorators North East Ltd | Administrative & support | 2015 |
| Delanoy Funeral Services Ltd | Other services | 2020 |
| Design and Security Services Limited | Manufacturing | 2004 |
| Detailed Groundworks Ltd | Construction | 2022 |
| Dimj Holdings Limited | Financial services | 2025 |
| Diskclock Limited | Wholesale & retail | 2005 |
| Distributor Supplies (UK) Limited | Administrative & support | 1997 |
| DJ Private Hire Ltd | Transport & logistics | 2021 |
| DJP (NE) Ltd | Transport & logistics | 2025 |
| DLI Seals Limited | Manufacturing | 2019 |
| Dnj.Electrical Ltd | Construction | 2020 |
| Doceclo Ltd | Wholesale & retail | 2025 |
| Domain Check Limited | Extraterritorial | 1999 |
| Dondav Limited | Hospitality | 2018 |
| Donnelly I Limited | Wholesale & retail | 2024 |
| Doski Group Prestige Autos Ltd | Wholesale & retail | 2021 |
| Dotty About Design Ltd | Professional & scientific | 2016 |
| DR Joseph Chandy Charitable Trust | Health & social care | 2012 |
| Dreamcatcherleisurene Ltd | Wholesale & retail | 2023 |
| Dreams Furnishing Limited | Wholesale & retail | 1999 |