| CNC Business Consultancy Limited | Professional & scientific | 2016 |
| CNJ Hotels Limited | Hospitality | 2025 |
| Co-Op Dancing Classes Limited | Arts & recreation | 2009 |
| Co.Lab Hair Creatives Limited | Other services | 2022 |
| CO13 Limited | Households | 2018 |
| Coach Trevi Limited | Information & communication | 2019 |
| Coaching Winners Limited | Administrative & support | 2020 |
| Coal City Barbers and Beauty Ltd | Other services | 2019 |
| Coast and Country Hospitality Group Limited | Financial services | 2025 |
| Coastal Cleaning Co. (Felixstowe) Limited | Extraterritorial | 2008 |
| Coastal DCC Ltd | Wholesale & retail | 2015 |
| Coastal Grid Homes Limited | Real estate | 2026 |
| Coastal Home Solutions Ltd | Construction | 2023 |
| Coastkini Ltd | Wholesale & retail | 2018 |
| Cobago Limited | Financial services | 2014 |
| Cobbett Investments Ltd | Financial services | 2025 |
| Cobblers Capel Ltd | Hospitality | 2023 |
| Cobbold & Godbold Limited | Construction | 2000 |
| Cobbold Management Services Limited | Households | 2004 |
| Cobra Properties Ltd | Real estate | 2017 |
| Cochengo Ltd | Information & communication | 2025 |
| Cocity Development Ltd | Financial services | 2019 |
| Cocity Holding Ltd | Financial services | 2021 |
| Cocity Operations Ltd | Financial services | 2021 |
| Cocksedge & Co. Limited | | 1925 |
| Coco Lash Ltd | Other services | 2023 |
| Coco Travel Limited | Transport & logistics | 2019 |
| COD Trans Ltd | Transport & logistics | 2018 |
| Code Brain Studio Limited | Information & communication | 2025 |
| CODE0 IT Consultancy Limited | Information & communication | 2019 |
| Cofco International UK Ltd | Agriculture & fishing | 1920 |
| Coff Holdings Limited | Professional & scientific | 1974 |
| Coffee Craft N Moore Ltd | Wholesale & retail | 2024 |
| Coffeelink Ltd. | Wholesale & retail | 2005 |
| Coffey Holdings Limited | Financial services | 2025 |
| Coffypan Selling Coffee and Beverages on Bike Ltd | Wholesale & retail | 2021 |
| Cofiso Limited | Financial services | 2006 |
| Cogent Technology Limited | Manufacturing | 1984 |
| Cognicloud Ltd | Information & communication | 2025 |
| Cognicode Solutions Ltd | Information & communication | 2023 |
| Cognitics Consulting Limited | Information & communication | 2010 |
| Cognitics Resources Ltd | Real estate | 2023 |
| Cognitio Consulting Ltd | Professional & scientific | 2025 |
| Coild Ltd | Financial services | 2026 |
| Coils N Curls Ltd | Other services | 2024 |
| Colborn Properties Limited | Real estate | 1993 |
| Colchester Business Park 750 Management Limited | Real estate | 2007 |
| Colchester Business Park 800 Management Limited | Real estate | 2000 |
| Colchester Dance HQ Ltd | Arts & recreation | 2017 |
| Colchester Health & Beauty Company Limited | Wholesale & retail | 2017 |
| Colchester Road Residential Home Limited | Health & social care | 2022 |
| Colchester Tyre & Exhaust Centre Limited | Wholesale & retail | 1997 |
| Colchester Tyre Centre (MOT) Limited | Wholesale & retail | 2005 |
| Colchester Valeting Ltd | Other services | 2021 |
| Colchurch Properties Limited | Other services | 2013 |
| Cold Steel Ltd | Information & communication | 2011 |
| Coldavian Ltd | Manufacturing | 2006 |
| Colding Group Ltd | Construction | 2024 |
| Cole & Sons Plumbing & Heating Ltd. | Construction | 2015 |
| Coles Cranes Group Limited(The) | Administrative & support | 1984 |
| Coletrader Ltd | Wholesale & retail | 2019 |
| Colin Ross Financial Planning Ltd | Financial services | 2017 |
| Collana Limited | Real estate | 2017 |
| College Convenience Store Ltd | Wholesale & retail | 2025 |
| College Gateway Limited | Wholesale & retail | 2017 |
| Collett Scaffolding Ltd | Construction | 2023 |
| Collinshandyman Ltd | Administrative & support | 2025 |
| Colne Contracts Limited | Construction | 2007 |
| Colne Gardens Management Company Limited | Households | 2016 |
| Colne Meadow (Brightlingsea) Management Company Limited | Households | 2019 |
| Colne Valley Commercial Services Limited | Hospitality | 1999 |
| Colnesett (East Anglia) Limited | Construction | 2015 |
| Colombo 7 Limited | Wholesale & retail | 2024 |
| Colors of Hope Studios Limited | Manufacturing | 2025 |
| Colour Wheel Worcester Limited | Education | 2019 |
| Colourplan Print & Design Limited | Manufacturing | 1992 |
| Colourways Decorators Ltd | Construction | 2014 |
| Colt Carpentry and Building Limited | Construction | 2016 |
| Colthill Properties Limited | Real estate | 1976 |
| Coltway Properties Limited | Real estate | 1981 |
| Columbo Software Ltd | Financial services | 2021 |
| Columbus Plumbing & Heating Services Limited | Construction | 2008 |
| Colwise Limited | Real estate | 1996 |
| COM FIN Solutions Limited | Financial services | 2019 |
| Combat Paintball Limited | Arts & recreation | 2003 |
| COMBAT2 Limited | Manufacturing | 2026 |
| COMBAT2COFFEE C.I.C. | Manufacturing | 2018 |
| Combination Construction Ltd | Construction | 2004 |
| Combined Property Home Limited | Real estate | 1985 |
| Combs Accountancy Limited | Professional & scientific | 2012 |
| Come Hither Design Limited | Professional & scientific | 2007 |
| Comfort Intuitive Ltd. | Manufacturing | 2008 |
| Comfortswork Ltd | Health & social care | 2024 |
| Comfy Daily Essentials Ltd | Manufacturing | 2025 |
| Command Development Ltd | Real estate | 2018 |
| Commerce OPS Ltd | Professional & scientific | 2026 |
| Commercial Clean Limited | Administrative & support | 2010 |
| Commercial Contract Tyres Limited | Wholesale & retail | 2001 |
| Commercial Financial Services Limited | Professional & scientific | 2014 |
| Commercial Industrial Estate Management Ltd. | Administrative & support | 2002 |