| Complex Support Anglia Ltd | Health & social care | 2023 |
| Compliance and Training Solutions Limited | Financial services | 2005 |
| Complyon Ltd | Information & communication | 2025 |
| Composite Sales Limited | Extraterritorial | 2022 |
| Compudata Limited | Real estate | 1972 |
| Compudoug Services Limited | Information & communication | 2005 |
| Computers Inc Limited | Wholesale & retail | 2010 |
| Computingpro Ltd | Information & communication | 2009 |
| Comtrac Landscape Ltd | Professional & scientific | 2024 |
| CONCEPT2COMPLETE Ltd | Administrative & support | 2026 |
| Conceptua Tuning Ltd | Wholesale & retail | 2015 |
| Concise Advice Limited | Information & communication | 2008 |
| Concordia Residential Limited | Real estate | 2018 |
| Concur Estate Agents Ltd | Real estate | 2022 |
| Concur Recruiters Ltd | Administrative & support | 2019 |
| Concurrent Technologies PLC | Manufacturing | 1985 |
| Coneco Limited | Real estate | 2004 |
| Confidence Energy Central Asia Ltd | Extraterritorial | 2008 |
| Conlon Surfacing Limited | Construction | 2025 |
| Connect Contract Services Limited | Construction | 2007 |
| Connected Consultancy Services Ltd | Professional & scientific | 2024 |
| Connecto Limited | Administrative & support | 1999 |
| Connexus Aviation Ltd | Transport & logistics | 2025 |
| Conor Carlin Properties Ltd | Real estate | 2026 |
| Conpro Limited | Construction | 1992 |
| Conquer Media Group Ltd | Information & communication | 2026 |
| Conscious Sedation Services Limited | Health & social care | 2016 |
| Consensus (2013) Limited | Health & social care | 2013 |
| Consensus 2013 Properties Limited | Health & social care | 2016 |
| Consensus Community Support Limited | Health & social care | 2008 |
| Consensus Group Holdings Limited | Financial services | 2020 |
| Consensus Henson Limited | Extraterritorial | 2015 |
| Consensus Holdco Limited | Financial services | 2013 |
| Consensus Newco Limited | Extraterritorial | 2013 |
| Consensus Properties 1 Limited | Health & social care | 2018 |
| Consensus Support Services Limited | Health & social care | 2000 |
| Conservacare Ltd | Construction | 2014 |
| Consigliere Limited | Professional & scientific | 2010 |
| Consolidated Infrastructure Limited | Professional & scientific | 2015 |
| Constable & Co Limited | Wholesale & retail | 2025 |
| Constable Chase (Colchester) Management Company Limited | Households | 2003 |
| Constable Heating Limited | Construction | 2025 |
| Constable VAT Consultancy LLP | | 2005 |
| Constable's Automotive Repair Specialist Ltd | Wholesale & retail | 2017 |
| Constantine Property Investments Ltd | Real estate | 2017 |
| Constellation Marketing Limited | Other services | 2011 |
| Construction (Consultancy Services) Suffolk Ltd | Construction | 2024 |
| Construction Chemicals Marketing Limited | Administrative & support | 2019 |
| Construction Development and Design (Investments) Limited | Real estate | 1999 |
| Construction Development and Design Limited | Construction | 1990 |
| Construction Fyself Ltd | Construction | 2024 |
| Construction IMC Ltd | Construction | 2026 |
| Consultify IT Ltd | Information & communication | 2024 |
| Contact Healthcare 24 Hours Limited | Administrative & support | 2019 |
| Container Wing Ltd | Professional & scientific | 2018 |
| Contel Solutions Limited | Wholesale & retail | 2014 |
| Contemporary Spaces Online Limited | Extraterritorial | 2016 |
| Contented Ltd | Information & communication | 2000 |
| Context Education Limited | Education | 2015 |
| Context Health Limited | Information & communication | 2015 |
| Context Properties Limited | Real estate | 1988 |
| Contigo Associates Ltd | Professional & scientific | 2017 |
| Continental Environmental Services Limited | Professional & scientific | 2010 |
| Continental Investment and International Legal Services Limited | Financial services | 2012 |
| Contractor Accounting Services Limited | Professional & scientific | 2018 |
| Contractors South Ltd | Construction | 2022 |
| Contrarian Group Limited | Information & communication | 2009 |
| Contrarian Properties Limited | Other services | 2007 |
| Control Online Limited | Wholesale & retail | 2022 |
| Controlq Ltd | Professional & scientific | 2026 |
| Controls Management Ltd | Construction | 2021 |
| Controlspec Commercial Cleaning Ltd | Administrative & support | 2026 |
| Convenet Ltd | Information & communication | 2020 |
| Convenient Cleaning and Removals Ltd | Transport & logistics | 2023 |
| Convolvulus Limited | Professional & scientific | 1998 |
| Cooch & Associates Limited | Professional & scientific | 2013 |
| Cook & Dunn Property Ltd | Real estate | 2019 |
| Cook and Long Limited | Construction | 2005 |
| Cook and Phillips Limited | Other services | 2013 |
| Cook Builders & Developments Ltd | Construction | 2016 |
| Cook Building Limited | Construction | 2025 |
| Cookies Enterprises Ltd | Manufacturing | 2025 |
| Cooks Agricultural Engineering Limited | Manufacturing | 2017 |
| Cooks Countryside Ltd | Administrative & support | 2020 |
| Cooks Creative Services Limited | Professional & scientific | 2026 |
| Cooks Properties (West Mersea) Limited | Real estate | 2017 |
| Cool Blue Developments Ltd | Real estate | 2017 |
| Cooley Design Ltd | Administrative & support | 2007 |
| Cooper & Brome (Contracts) Limited | Construction | 1988 |
| Cooper 2015 Management Ltd | Professional & scientific | 2016 |
| Cooper Cambridge Ltd | Financial services | 2023 |
| Cooper GAS Ltd | Construction | 2021 |
| Cooperheims Limited | Real estate | 2020 |
| Coopers Groundworks & Civil Engineering Ltd | Construction | 2022 |
| Copeman Properties Limited | Real estate | 2011 |
| Copford Investment Holdings Private Ltd | Financial services | 2021 |
| Copford Investment Private Limited | Hospitality | 2024 |
| Copford Investments Private Ltd | Hospitality | 2021 |
| Copford Plumbing & Heating Ltd | Construction | 2014 |
| Cophee Club Limited | Hospitality | 2025 |