| Close Brothers Building & Maintenance Limited | Construction | 2004 |
| Close Brothers Rail Limited | Construction | 2004 |
| Close Homes Limited | Real estate | 2009 |
| Cloudminded Engineering Ltd | Information & communication | 2022 |
| Clough Lane Cafe Ltd | Hospitality | 2019 |
| CLS Training Ltd | Education | 2022 |
| Club Divers Limited | Construction | 2015 |
| Clydesdale Construction Limited | Construction | 2003 |
| CM Lawns Ltd | Administrative & support | 2020 |
| Cmac Cleaning Solutions Ltd | Administrative & support | 2023 |
| CML Environmental Services Ltd | Construction | 2014 |
| CMZ Developments Limited | Construction | 2022 |
| CMZ Group Limited | Financial services | 2022 |
| CNE Solutions Ltd | Manufacturing | 2024 |
| CNJ Holdings Ltd | Other services | 2024 |
| Cnsltnt Ltd | Professional & scientific | 2004 |
| Coachman's Mews Management Company Limited | Households | 2015 |
| Coatings Tech Ltd | Professional & scientific | 2017 |
| Coatings Technology Ltd | Other services | 2016 |
| Coco Pictures Limited | Information & communication | 2017 |
| Cocoa Research (UK) Limited | Professional & scientific | 1996 |
| Cocoa Research Association Limited(The) | Professional & scientific | 1973 |
| Codi Fire Ltd | Public administration | 2020 |
| Codos Creative Limited | Professional & scientific | 2015 |
| COE & Co Limited | Construction | 2022 |
| Coflux Services Limited | Administrative & support | 2012 |
| Cogley Structural Solutions Ltd | Professional & scientific | 2020 |
| Cognozent Tech Limited | Construction | 2022 |
| Colin Peacock Limited | Construction | 1972 |
| Colin's Cars Ltd | Transport & logistics | 2003 |
| Collectible Corner Limited | Wholesale & retail | 2022 |
| Collette Connect Ltd | Health & social care | 2022 |
| Colossal Copy Ltd | Professional & scientific | 2025 |
| Columbia-Staver Limited | Manufacturing | 1974 |
| Commercial Support Systems Limited | Professional & scientific | 1997 |
| Commercial Vehicle Support Ltd | Wholesale & retail | 2021 |
| Common Knowledge Limited | Information & communication | 2003 |
| Commotion Studios Limited | Information & communication | 2004 |
| Community Lottery Schemes Limited | Financial services | 2010 |
| Complete Access Flooring Ltd | Construction | 2018 |
| Complete Building & Landscapes Ltd | Construction | 2025 |
| Complete Developments Essex Limited | Construction | 2014 |
| Complete Technical Surveys Ltd | Real estate | 2004 |
| Completely Clear Limited | Water & waste | 2017 |
| Compucharge Limited | Manufacturing | 2003 |
| Comtrans Haulage Ltd | Transport & logistics | 2019 |
| Concept & Printing International Limited | Administrative & support | 2014 |
| Concept Filming Limited | Information & communication | 2008 |
| Concept Properties London Limited | Real estate | 2023 |
| Conferdents Limited | Health & social care | 2015 |
| Construct & Develop (U.K) Limited | Construction | 2021 |
| Construct + Develop Limited | Construction | 2024 |
| Construction Awareness Ltd | Construction | 2024 |
| Construction DNA Ltd | Information & communication | 2025 |
| Construction House Consult Ltd | Administrative & support | 2017 |
| Consultancy Design Incorporated Ltd | Information & communication | 2023 |
| Coopers Hawk Solutions Limited | Health & social care | 2021 |
| Copper POT Leamington Ltd | Hospitality | 2025 |
| Copperlynx Computer Services Limited | Information & communication | 2008 |
| Core IP Holdings Limited | Financial services | 2025 |
| Corinthian Court Management Limited | Households | 2020 |
| Coronation Court RTM Company Ltd | Households | 2020 |
| Corringham Cryo Ltd | Health & social care | 2024 |
| Cortes Auto Group England Ltd | Wholesale & retail | 2016 |
| Cotex Global Services Limited | Transport & logistics | 2026 |
| Country Flooring (Essex) Limited | Wholesale & retail | 2001 |
| County Access Plant Hire Limited | Construction | 2014 |
| County Ales Limited | Hospitality | 2015 |
| County Corporation Limited | Other services | 2021 |
| Courtenay Brickwork Limited | Construction | 2015 |
| Cowrie Road Ltd | Wholesale & retail | 2020 |
| Cozy Energy Ltd | Manufacturing | 2017 |
| CP (LSS) Limited | Professional & scientific | 2005 |
| CP (WBL) Limited | Professional & scientific | 2005 |
| Cproperty Holdings Limited | Real estate | 2024 |
| Cpsdj Services Ltd | Information & communication | 2026 |
| Craft Property Ventures Ltd | Real estate | 2018 |
| Craft Skills Ltd | Education | 2023 |
| Craig Jordan Limited | Information & communication | 2023 |
| Craigfield Limited | Wholesale & retail | 2011 |
| Craintern (UK) Limited | Manufacturing | 2003 |
| Cranfield Realty Limited | Real estate | 2022 |
| Cranham Dental Centre Ltd | Health & social care | 2011 |
| Crawford Enterprises Limited | Construction | 1998 |
| Create Business Limited | Real estate | 2019 |
| Creative Boomerang Ltd | Information & communication | 2015 |
| Creative Construct Solution Ltd | Manufacturing | 2018 |
| Creative Glass Care Limited | Manufacturing | 2020 |
| Creative Stone Company (Essex) Ltd | Construction | 2014 |
| Creativity Hub Promotions Limited | Arts & recreation | 2022 |
| Crestwood Holdings Limited | Real estate | 1994 |
| Crestwood UK Limited | Wholesale & retail | 2008 |
| Crew Digital Limited | Information & communication | 2026 |
| Criciuma Ltd | Other services | 2017 |
| Crondon Storage Services Limited | Transport & logistics | 2002 |
| Cross Creative Solutions Limited | Professional & scientific | 2024 |
| Crouch Vale Cars Limited | Wholesale & retail | 2011 |
| Crouch Valley Group Ltd | Financial services | 2026 |
| Crouch Valley Kitchen Ltd | Extraterritorial | 2026 |
| Crouch Valley Nutrition Ltd | Extraterritorial | 2026 |