| Christian Bowen Hygiene Support Ltd | Professional & scientific | 2024 |
| Chronic Insights Ltd | Information & communication | 2018 |
| Chuangling Ltd | Professional & scientific | 2023 |
| Chuck Tails Ltd | Other services | 2024 |
| Churchill Garage Doors Limited | Construction | 2010 |
| Cian Creative PR Limited | Extraterritorial | 2011 |
| Cinars Trade Ltd | Wholesale & retail | 2025 |
| Cinders Prom Bridal and Occasion Wear Ltd | Wholesale & retail | 2019 |
| Citizen Songwriters C.I.C. | Arts & recreation | 2018 |
| City Civils Limited | Construction | 2022 |
| Civils Solutions North East Limited | Construction | 2026 |
| CJS & Partners Ltd | Real estate | 2013 |
| CKI UK Co 5 Limited | Financial services | 2011 |
| CKI UK Co 6 Limited | Financial services | 2011 |
| CLA GAS Limited | Energy | 2026 |
| Clanoco Ltd | Real estate | 2025 |
| Clapham Holiday Park Limited | Hospitality | 2025 |
| Clare Holdings Ltd | Real estate | 2024 |
| Claritec Ltd | Information & communication | 2020 |
| Clark Degnan Limited | Professional & scientific | 2015 |
| Clark's Taxis Limited | Transport & logistics | 2007 |
| Clarkson Collective Limited | Professional & scientific | 2026 |
| Class Assets UK Ltd | Real estate | 2025 |
| Classic and Retro Autos Limited | Wholesale & retail | 2015 |
| Classic Solutions Engineering Limited | Manufacturing | 2008 |
| Claypath Properties Limited | Households | 2018 |
| Claypath Restaurant Ltd | Hospitality | 2024 |
| Claypathlease by JHJ Ltd | Real estate | 2026 |
| Cleaned Right NE Limited | Administrative & support | 2021 |
| Cleanrite High-Pressure Cleaning Ltd | Administrative & support | 2017 |
| Cleanwaste AI Ltd | Information & communication | 2024 |
| Clear Cavity UK Limited | Construction | 2025 |
| Clear Desk Solutions Ltd | Administrative & support | 2025 |
| Clear Drain (North East) Ltd | Water & waste | 2022 |
| Clear Link Solutions Ltd | Professional & scientific | 2025 |
| Clearflow Plumbing and Heating NE Limited | Construction | 2025 |
| Clearflow Radiators Limited | Manufacturing | 1995 |
| Clearpathnetwork Ltd | Wholesale & retail | 2025 |
| Cleartrans Limited | Extraterritorial | 2014 |
| Clearview NE Ltd | Administrative & support | 2026 |
| Clearwater Gill Limited | Administrative & support | 2021 |
| Clennell Holdings Ltd | Financial services | 2025 |
| Climate Action Durham Community Interest Company | Other services | 2021 |
| Climate Action North Community Interest Company | Professional & scientific | 2017 |
| Climate Change Heritage CIC | Professional & scientific | 2022 |
| Climax Technology Limited | Wholesale & retail | 2007 |
| CLL Demir Ltd | Wholesale & retail | 2025 |
| Clockwork Espresso (Holdings) Limited | Financial services | 2019 |
| Clockwork Espresso Ltd | Professional & scientific | 2014 |
| Cloud 9 Industries Ltd | Wholesale & retail | 2017 |
| Cloud Alloy Ltd | Information & communication | 2023 |
| Cloudgenie Limited | Information & communication | 2026 |
| Clovely Care Limited | Health & social care | 2009 |
| Clover 51 Limited | Manufacturing | 2012 |
| CLS250 Limited | Professional & scientific | 2023 |
| CLX Ltd | Hospitality | 2001 |
| Clyde NET Zero Limited | Construction | 2022 |
| CM Retro Limited | Wholesale & retail | 2019 |
| CM West Rainton Management Company Limited | Real estate | 2024 |
| CMA Electrical Limited | Construction | 2015 |
| CMB Logistics Ltd | Transport & logistics | 2022 |
| CMC Funding Ltd | Administrative & support | 2009 |
| Cmcroxford Ltd | Information & communication | 2019 |
| CMD Housing Solutions Limited | Professional & scientific | 2017 |
| CMI Music Limited | Wholesale & retail | 2015 |
| CMJ Plastering & Taping Ltd | Construction | 2024 |
| Cmlcnr Ltd | Wholesale & retail | 2025 |
| CN Labs Ltd | Wholesale & retail | 2023 |
| CNR Joinery Ltd | Construction | 2025 |
| Coach to Inspire Ltd | Professional & scientific | 2024 |
| Coached by DAN North East Ltd | Arts & recreation | 2023 |
| Coal 4 Energy Limited | Wholesale & retail | 2006 |
| Coalfield Studios Ltd | Information & communication | 2025 |
| Coarse Restaurant Ltd | Hospitality | 2021 |
| Coast to Coast Exotics Limited | Wholesale & retail | 2005 |
| Coates Butchers Ltd | Wholesale & retail | 2008 |
| Cocken Lodge Limited | Arts & recreation | 2025 |
| Coforged Ltd | Information & communication | 2026 |
| Cohost North East Ltd | Hospitality | 2025 |
| Colgar Accounting and Taxation Services Ltd | Professional & scientific | 2025 |
| Colin Hiles Consultancy Limited | Professional & scientific | 2019 |
| Colleagues on TAP Limited | Administrative & support | 2011 |
| Collected Books Limited | Wholesale & retail | 2021 |
| Collinson Taylor Capital Ltd. | Financial services | 2017 |
| Collision Assist UK Limited | Wholesale & retail | 2021 |
| Collvey Ltd | Information & communication | 2025 |
| Colonel Porters Emporium Limited | Hospitality | 2015 |
| Colors Taxis Ltd | Transport & logistics | 2006 |
| Colour Wheel County Durham Ltd | Education | 2018 |
| Colpitts Holdings Ltd | Financial services | 2026 |
| Comcore Ltd | Construction | 2017 |
| Comely Homes Limited | Real estate | 2020 |
| Comingnity CIC | Professional & scientific | 2024 |
| Comingnity Connect CIC | Information & communication | 2025 |
| Commercial Convenience Ltd | Wholesale & retail | 2020 |
| Commercial Mortgage Centre Limited | Administrative & support | 2004 |
| Commercial Solar Power UK Ltd | Construction | 2020 |
| Commonwealth Group Holdings Ltd | Financial services | 2025 |
| Commonwealth Group Investments Ltd | Financial services | 2025 |
| Commonwealth Group Real Estate Ltd | Financial services | 2025 |