| Comprehensive Property Maintenance Ltd | Energy | 2019 |
| COMPSON19 Ltd | Construction | 2017 |
| Compton Consulting Limited | Information & communication | 2024 |
| Computasolve Limited | Information & communication | 1988 |
| Comserv Limited | Information & communication | 1998 |
| Comsol Northern Ltd | Professional & scientific | 2012 |
| Comtek UK Limited | Information & communication | 2005 |
| Concept Care Solutions Limited | Health & social care | 2001 |
| Concept Design and Build Limited | Construction | 2004 |
| Concept Project B Ltd | Other services | 2013 |
| Concept UK Properties LLP | | 2006 |
| Concept UK Properties Loudwater LLP | | 2013 |
| Concepto EOT Limited | Professional & scientific | 2022 |
| Concepto Limited | Real estate | 2012 |
| Concepto Nipt Limited | Health & social care | 2022 |
| Concepts Management Limited | Real estate | 2012 |
| Concise Consultancy Services Ltd | Other services | 2015 |
| Concret Haulage Limited | Transport & logistics | 2024 |
| Condor Films Ltd | Information & communication | 2016 |
| Configured Group Limited | Administrative & support | 2024 |
| Confitential IT Services Ltd | Information & communication | 2019 |
| Congenial Realty Limited | Real estate | 2022 |
| Coni London Ltd | Construction | 2011 |
| Conifers (Garston) Residents Management Company Limited | Hospitality | 1989 |
| Conmach Limited | Financial services | 2018 |
| Connect Residentials Ltd | Real estate | 2023 |
| Connect Training and Wellbeing Services Ltd | Education | 2026 |
| Connection Plus Travel Europe Ltd | Administrative & support | 2024 |
| Connections (Group) Limited | Extraterritorial | 2025 |
| Connections Money Ltd | Professional & scientific | 2009 |
| Connolly's Estates & Holdings Ltd | Construction | 2022 |
| Connolly's Management & Maintenance Ltd | Real estate | 2017 |
| Connstruct Consultancy Services Ltd | Professional & scientific | 2017 |
| Conscience-Cobalt Limited | Manufacturing | 2017 |
| Conscious Culture Limited | Information & communication | 2025 |
| Conscious Drinks Limited | Manufacturing | 2018 |
| Conscious Living Health Ltd | Wholesale & retail | 2020 |
| Conscious Wealth Limited | Financial services | 2013 |
| Consept Accounting Solutions Ltd | Professional & scientific | 2011 |
| Consis Limited | Information & communication | 2013 |
| Consolidated Equities Limited | Real estate | 1954 |
| Consolidated Machinery (Mining) Co. Limited | Professional & scientific | 1962 |
| Consort Luxury Group Limited | Administrative & support | 2024 |
| Constant Estates Limited | Real estate | 1971 |
| Construct Resolve Limited | Professional & scientific | 2021 |
| Construct Techniques Limited | Professional & scientific | 2015 |
| Constructing Excellence Limited | Professional & scientific | 2003 |
| Construction and Development Services Limited | Construction | 2026 |
| Construction Engineering Management Solutions & Co. Limited | Construction | 2024 |
| Construction Management and Costings Limited | Construction | 2026 |
| Construction Training Center UK Ltd | Education | 2017 |
| Constructions by Mihai Limited | Construction | 2026 |
| Constructions R US Ltd | Construction | 2025 |
| Constructive Site Services Ltd | Professional & scientific | 2024 |
| Constructops Ltd | Construction | 2024 |
| Consult 2000 Consulting Limited | Construction | 2012 |
| Consult RF Limited | Information & communication | 2023 |
| Consulting Made Easy CIC | Professional & scientific | 2022 |
| Content London Limited | Professional & scientific | 2011 |
| Contino Foods Limited | Manufacturing | 2020 |
| CONTOUR886 Ltd | Manufacturing | 2005 |
| Contractor Umbrella Limited | Professional & scientific | 2001 |
| Contramax Logistics L.P. | | 2018 |
| Contrast Construction & Management Ltd | Construction | 2018 |
| Conventional Chaos Limited | Information & communication | 2014 |
| Convergent Solutions Limited | Information & communication | 2024 |
| Conversebsl Ltd | Education | 2024 |
| Conversion Concepts Limited | Construction | 2015 |
| Cook and Sing Limited | Hospitality | 2025 |
| Cookie Corner Ltd | Manufacturing | 2026 |
| Cookies & Cream Ltd | Information & communication | 2014 |
| Cooks Transport Engineers Limited | Wholesale & retail | 2002 |
| Cool Carrot Limited | Wholesale & retail | 2026 |
| Cool Form Limited | Energy | 2024 |
| Coolbain Limited | Real estate | 2008 |
| Coolstone Contractors Limited | Wholesale & retail | 2007 |
| Coomeet Limited | Professional & scientific | 2017 |
| Coomeet PAY Limited | Professional & scientific | 2017 |
| Cooper Associates Structural Engineers Limited | Construction | 2010 |
| Cooper Fencing Limited | Construction | 2025 |
| Cooper Moss Rutland LLP | | 2017 |
| Cooper Moss Rutland Projects Limited | Professional & scientific | 2021 |
| Cooper's Properties Limited | Real estate | 2018 |
| Coopers and Lloyds Ltd | Information & communication | 2020 |
| Coops CAN Take IT Ltd | Transport & logistics | 2025 |
| Coote Management Ltd | Information & communication | 2008 |
| Copper Kadai Watford Limited | Hospitality | 2026 |
| Copperfields Management (Harrow) Limited | Households | 1992 |
| Coppermill Lock (Harefield) Management Company Limited | Households | 2014 |
| Coracle Solutions Limited | Information & communication | 2018 |
| Coral Ace Business Solutions Limited | Information & communication | 2020 |
| Coral Club Limited | Administrative & support | 2022 |
| Coral Constructors Ltd | Construction | 1992 |
| Corale Property Investments Limited | Real estate | 2022 |
| Coram Consulting Limited | Other services | 2006 |
| Corbi LP | | 2017 |
| Corbins Lane Harrow Management Limited | Households | 2002 |
| Core Impression Limited | Information & communication | 2023 |
| Core International Marketing and Management Consultancy Ltd | Professional & scientific | 2017 |
| Core Quest Ltd | Education | 2026 |