| CHT Consultancy Ltd | Administrative & support | 2022 |
| CHT Houses Ltd | Real estate | 2025 |
| Church Farm (High Street Lakenheath) Management Company Limited | Households | 2008 |
| Churchman House Residents Management Company Limited | Households | 2000 |
| Circularify Ltd | Information & communication | 2022 |
| Cirrus Group Ltd | Wholesale & retail | 2024 |
| CJ Consultancy Services Ltd. | Professional & scientific | 2020 |
| Clare Bears Community Pre-School Limited | Education | 2017 |
| Clark & SON Butchers Ltd | Wholesale & retail | 2020 |
| Clark & Willcocks Limited | Real estate | 1992 |
| Clark and Eves Ltd | Construction | 2014 |
| Clark Digital Services Limited | Information & communication | 2012 |
| Clarke's Bakery Ltd | Manufacturing | 2023 |
| Clarks Advanced Shredding Limited | Water & waste | 2009 |
| Clarks Archive Storage Limited | Transport & logistics | 1996 |
| Clark’S Courier Services Ltd | Transport & logistics | 2025 |
| Clayoh Limited | Professional & scientific | 2025 |
| Clayton Records Ltd | Information & communication | 2021 |
| CLB Recruitment Solutions Limited | Transport & logistics | 2013 |
| Clearance Warehouse Ltd | Wholesale & retail | 2026 |
| Clement Clarke Communications Limited | Other services | 2015 |
| Climatherm Limited | Construction | 2021 |
| Clip Sound and Music CIC | Education | 2019 |
| CM Defence Ltd | Professional & scientific | 2025 |
| Cmac Specialists Limited | Professional & scientific | 2014 |
| Cmon Holdings Limited | Wholesale & retail | 2023 |
| CN Contracts Limited | Administrative & support | 2016 |
| CNG Brickwork Limited | Construction | 2019 |
| CO10 Scaffolding Limited | Construction | 2026 |
| Coalesce Consulting Limited | Professional & scientific | 2018 |
| Coast 2 Coast Training Ltd | Education | 2025 |
| Coast Dorset Management Company Limited | Households | 2020 |
| Coastal Limited | Manufacturing | 2007 |
| Coastal Windows Limited | Construction | 2004 |
| Cochrane Productions Ltd | Information & communication | 2025 |
| Cockx Sudbury Limited | Manufacturing | 1987 |
| Codsal Limited | Hospitality | 2022 |
| Cole Trading Limited | Transport & logistics | 2024 |
| Collective Interiors Ltd | Construction | 2023 |
| Colne Engaine Wraparound Care Ltd | Health & social care | 2021 |
| Colne Valley Marquees Limited | Administrative & support | 2024 |
| Combi Catering Engineers Ltd | Professional & scientific | 2019 |
| Command Pest Control Limited | Administrative & support | 1997 |
| Commission Projects Limited | Arts & recreation | 2012 |
| Commonholder Angels Limited | Professional & scientific | 2021 |
| Companion Pet Services Ltd | Education | 2023 |
| Company 625 Limited | Other services | 2012 |
| Company 627 Limited | Real estate | 2018 |
| Complete Gleam Ltd | Administrative & support | 2020 |
| Complete Holiday Lets Ltd | Other services | 2024 |
| Complete Maintenance & Cleaning Limited | Administrative & support | 2016 |
| Complete Properties Management Limited | Real estate | 2025 |
| Configua Limited | Administrative & support | 2018 |
| Connexa Networks Limited | Real estate | 2007 |
| Considered Risks Limited | Information & communication | 2010 |
| Construct Reason Limited | Construction | 1980 |
| Construction IBS Ltd | Construction | 2023 |
| Contact Sports Specialists Limited | Wholesale & retail | 1998 |
| Convivial PUB Company Limited | Hospitality | 2014 |
| Cool OUT Ltd | Wholesale & retail | 2008 |
| Coombelands Gardens (Addlestone) Management Company Ltd | Households | 2019 |
| Corporate Security Consulting Ltd | Professional & scientific | 2019 |
| Cotherm (UK) Limited | Manufacturing | 1986 |
| Cotton on Limited | Information & communication | 2014 |
| Counter Intrusive Technology Ltd | Information & communication | 2018 |
| Courtwood Properties Limited | Administrative & support | 2001 |
| Courtyard Venture and Hospitality Limited | Hospitality | 2026 |
| Coverite Upholstery Ltd | Other services | 2016 |
| Cowlin Plant Limited | Construction | 2026 |
| Cowrie Interiors Ltd | Professional & scientific | 2026 |
| Cox's Boxes Limited | Wholesale & retail | 2021 |
| CPC Microsystems Ltd | Information & communication | 2007 |
| CR Civils Ltd | Construction | 2024 |
| Cradle Foods C.I.C. | Wholesale & retail | 2016 |
| Craig Warner Limited | Arts & recreation | 2005 |
| Creative Colchester CIC | Information & communication | 2022 |
| Cremcetera Ltd | Manufacturing | 2023 |
| Cristalice Limited | Other services | 2020 |
| Croham Leigh Freehold Company Ltd | Households | 2012 |
| Crosbie Mechanical Services Ltd | Construction | 2020 |
| Cross Country Cattering Ltd | Professional & scientific | 2025 |
| Crown N Crust Ltd | Hospitality | 2026 |
| Crowning Glory London Limited | Manufacturing | 2018 |
| CRW Repairs Ltd | Manufacturing | 2019 |
| Crystal on HCW Ltd | Wholesale & retail | 2020 |
| CS East Anglia Ltd | Real estate | 2025 |
| CSC Car Service Centre Ltd | Wholesale & retail | 2025 |
| CSG Ceramic Tiling Limited | Construction | 2015 |
| CT Sudbury Limited | Hospitality | 2025 |
| Cteot Limited | Extraterritorial | 2024 |
| CTJ Transport Services Ltd | Transport & logistics | 2019 |
| CTS Aviation Ltd | Administrative & support | 2018 |
| Cubatics Ltd | Information & communication | 2016 |
| Cubitt Projects Limited | Real estate | 2003 |
| Cult Collection Online Ltd | Wholesale & retail | 2016 |
| Cursed Crypt Events Limited | Administrative & support | 2025 |
| Cutts Cousins Limited | Construction | 2013 |
| Cutts Property Ltd | Real estate | 2025 |
| Cwebdesign Ltd | Professional & scientific | 2025 |
| CWF Events Limited | Hospitality | 2024 |