| Cobalt Central Coffee and Deli Limited | Hospitality | 2020 |
| Cobalt Scaffolding Limited | Construction | 2015 |
| Comakers Ltd | Information & communication | 2026 |
| Comcentrex Limited | Information & communication | 2009 |
| Commando Performance Ltd | Arts & recreation | 2022 |
| Commercial Boiler Solutions Ltd | Administrative & support | 2020 |
| Common Sense Properties Ltd | Real estate | 2021 |
| Communityedpsych Ltd | Education | 2025 |
| Compass Navigating Excellence Ltd | Education | 2012 |
| Complete Facilities North East Limited | Administrative & support | 2013 |
| Connect Ponies CIC | Education | 2025 |
| Connell Holding Limited | Administrative & support | 2023 |
| Connelly Furniture Ltd | Manufacturing | 2023 |
| Connor Reilly Ltd | Manufacturing | 2019 |
| Consulting Pulsar Ltd | Information & communication | 2025 |
| Contract Solution Management Ltd | Construction | 2013 |
| Controle Mesure Regulation (UK) Limited | Manufacturing | 1984 |
| Core Industrial Services Limited | Wholesale & retail | 2017 |
| Core Security Services NE Ltd | Administrative & support | 2022 |
| Cornermark Group Ltd | Real estate | 2025 |
| Costcutter (Howden) Limited | Other services | 2007 |
| Countonpeddie Limited | Administrative & support | 2013 |
| County Window Cleaning Services Limited | Administrative & support | 2013 |
| Covermead Limited | | 1980 |
| Covert Solutions Ltd | Administrative & support | 2025 |
| CP Designs Ltd | Manufacturing | 2019 |
| CPD Rigging and Lifting Ltd | Mining & quarrying | 2015 |
| Crab and Compass Limited | Wholesale & retail | 2018 |
| Craig Gospell Joinery Ltd | Construction | 2025 |
| Craig Scorf Fencing & Decking Ltd | Administrative & support | 2023 |
| Craig Scorf Patios & Driveways Ltd | Construction | 2023 |
| Craig Scorf Properties Ltd | Real estate | 2024 |
| Crane Workers Limited | Construction | 2020 |
| CRE8NRG Ltd | Energy | 2024 |
| Creatimo Ltd | Wholesale & retail | 2022 |
| Creative Indoor Play Limited | Arts & recreation | 2010 |
| Crestview & PT Limited | Information & communication | 2025 |
| Cris&Mady Ltd | Transport & logistics | 2017 |
| Crywolf Pool Tables Ltd | Real estate | 2025 |
| CT Joinery Ltd | Manufacturing | 2022 |
| Cube Performance Academy CIC | Health & social care | 2025 |
| Cuenet Limited | Information & communication | 2022 |
| Cullercoats Brewery Limited | Manufacturing | 2011 |
| Curedu Consulting Limited | Professional & scientific | 2011 |
| Cushty Leisure Ltd | Hospitality | 2026 |
| D Balmer & Sons Ltd | Transport & logistics | 2014 |
| D Corke Civil Engineering Limited | Construction | 2015 |
| D J Mcdonald Inspections Ltd | Professional & scientific | 2018 |
| D P Engineering Solutions Limited | Administrative & support | 2014 |
| D Tomaselli Limited | Wholesale & retail | 2015 |
| D&J Property Neast Limited | Households | 2021 |
| D&M Property Improvements Ltd | Real estate | 2025 |
| D.Moore Energy Limited | Professional & scientific | 2018 |
| D.S.Fashion U.K. Ltd | Manufacturing | 2003 |
| Daisymama Limited | Hospitality | 2024 |
| Dalstone Ltd | Professional & scientific | 2021 |
| Dandi Stays Ltd | Hospitality | 2022 |
| Danielle Hodgson Ltd | Other services | 2025 |
| Danil Barber Ltd | Other services | 2022 |
| Dannor Energy Services Ltd | Professional & scientific | 2024 |
| Daravent Integrated Ltd | Hospitality | 2025 |
| Dark Matter Aesthetics Ltd | Other services | 2021 |
| Dasc Properties Limited | Real estate | 2016 |
| David Whittle Property Ltd | Real estate | 2024 |
| Dawn Michelle Ltd | Wholesale & retail | 2026 |
| DC Composite Solutins Ltd | Construction | 2023 |
| DC Hair Studios Ltd | Other services | 2019 |
| DC Offshore Engineering Ltd | Manufacturing | 2021 |
| Dcoull Ltd | Hospitality | 2025 |
| DD Inspection Services NE Limited | Professional & scientific | 2018 |
| DEC Spec Limited | Wholesale & retail | 2020 |
| Deetar Limited | Wholesale & retail | 2024 |
| Deneview Ltd | Professional & scientific | 2019 |
| Dennis & Dill Mechanical Ltd | Manufacturing | 2026 |
| Design Gates Online Ltd | Manufacturing | 2026 |
| Desma Ltd | Transport & logistics | 2025 |
| Dfab Marine Limited | Transport & logistics | 2020 |
| DG Capital Group Limited | Information & communication | 2025 |
| DH Joinery & Carpentry Ltd | Construction | 2025 |
| DHG Build Solutions Limited | Construction | 2018 |
| DHG Electrical Solutions Ltd | Construction | 2024 |
| DHT Solutions NE Ltd | Construction | 2025 |
| Diconvergence Ltd | Real estate | 2025 |
| Didia Foods Limited | Hospitality | 2023 |
| Digital 9 Seaedge Limited | Financial services | 2021 |
| Digital Innovation Skills Hub C.I.C. | Professional & scientific | 2026 |
| Dine at Home Takeaway Ltd | Hospitality | 2024 |
| Diomede Sciences Ltd | Professional & scientific | 2025 |
| Direct Air Conditioning & Refrigeration Co Ltd | Energy | 2014 |
| Direct Employment Solutions Ltd | Professional & scientific | 2025 |
| Direct Living Space Ltd | Real estate | 2016 |
| Displaced Digital Limited | Information & communication | 2025 |
| DJ Brickworks Ltd | Administrative & support | 2025 |
| DJ Paint and Decorating Ltd | Construction | 2025 |
| DJA Coating Limited | Administrative & support | 2020 |
| Djkvape Ltd | Wholesale & retail | 2014 |
| DL Plastering (NE) Ltd | Construction | 2025 |
| DL Wind Services Ltd | Professional & scientific | 2025 |
| DM Property & Maintenance Ltd | Real estate | 2020 |
| Dogcult Ltd | Other services | 2025 |