| Claydon Court Residents Association Limited | Households | 1987 |
| Clear Box Analytics Ltd | Information & communication | 2019 |
| Clear Waste Recycling Ltd | Water & waste | 2020 |
| Clearwater Analytics, Ltd | Financial services | 2012 |
| Cletus Ltd | Information & communication | 2023 |
| Clever Management Solutions Limited | Professional & scientific | 2008 |
| Clieveden Estates Ltd | Real estate | 2019 |
| Climatrol Limited | Information & communication | 2009 |
| Clockwork Communications (London) Limited | Professional & scientific | 1996 |
| Cloud Glare IT Solutions Limited | Information & communication | 2022 |
| Cloud Technologist Limited | Information & communication | 2022 |
| Cloudadept Systems Limited | Information & communication | 2009 |
| Clustrix Global Ltd | Information & communication | 2026 |
| Cmapp Limited | Information & communication | 2012 |
| CMC Corporation Ltd | Administrative & support | 2023 |
| CMH Fabrications Limited | Manufacturing | 2008 |
| Coast Active Ltd | Real estate | 2000 |
| Cocoon Kids - Creative Counselling and Play Therapy CIC | Wholesale & retail | 2021 |
| Coffee Genius Ltd | Manufacturing | 2023 |
| Coffee Hunter Limited | Professional & scientific | 2001 |
| Coggins Joinery Ltd | Construction | 2024 |
| Cognix Digital Limited | Information & communication | 2026 |
| Colescrete Construction Limited | Construction | 2008 |
| Collin Street Bakery Limited | Hospitality | 2018 |
| Colney DM Ltd | Construction | 2019 |
| Colour Roll Ltd | Arts & recreation | 2026 |
| Colourful White Ltd | Wholesale & retail | 2025 |
| Combined Sports Coaching Ltd | Education | 2025 |
| Comfort DEN Limited | Hospitality | 2019 |
| Comma Consulting UK Limited | Other services | 2009 |
| Common Holdings Limited | Financial services | 2016 |
| Communicards Ltd | Arts & recreation | 2023 |
| Companion Logistics Limited | Transport & logistics | 2024 |
| Compassionate Eyes Limited | Other services | 2025 |
| Compcheq Ltd | Information & communication | 2020 |
| Complete Sash Window Company Ltd | Construction | 2009 |
| Complex Versus Complicated Ltd | Professional & scientific | 2026 |
| CON Fire and Security Limited | Construction | 2020 |
| Concept Telecom Services Ltd | Information & communication | 2019 |
| Connected by Silk Limited | Manufacturing | 2021 |
| Connected Stars Limited | Health & social care | 2020 |
| Connoisseur International Distribution Limited | Transport & logistics | 1997 |
| Conocimiento Ltd | Professional & scientific | 2025 |
| Conolly IT Consulting Limited | Information & communication | 2025 |
| Controlled Logistics 24 Ltd | Transport & logistics | 2024 |
| Convenience Stop Limited | Wholesale & retail | 2020 |
| Coolurself Ltd | Construction | 2022 |
| Coppermill Accounting Ltd. | Professional & scientific | 1996 |
| Copsem Lane Limited | Construction | 2022 |
| Core Teamwear Limited | Wholesale & retail | 2025 |
| Core UK Trading Limited | Other services | 2014 |
| Cornel's Creations Ltd | Manufacturing | 2023 |
| Corneli's Limited | Construction | 2022 |
| Corporate Life Skills Ltd. | Administrative & support | 2011 |
| Corvette Surveying Services Limited | Construction | 2015 |
| Costello Bespoke Ltd | Manufacturing | 2007 |
| Costilloes Limited | Professional & scientific | 2024 |
| Country House Nursing & Retirement Homes Limited | Health & social care | 1986 |
| Courtney Properties Ltd | Real estate | 2024 |
| CR Supplies Ltd | Wholesale & retail | 2025 |
| CRA Parent Limited | Administrative & support | 2012 |
| Crafranci Ltd | Wholesale & retail | 2025 |
| Crafty Designs Ltd | Manufacturing | 2022 |
| Cranston Heating & Plumbing Ltd | Construction | 2018 |
| Crash Override Ltd | Information & communication | 2022 |
| Craveecorner Ltd | Hospitality | 2025 |
| Creative Hive Marketing Limited | Information & communication | 2025 |
| Crescendo Brand Events Limited | Extraterritorial | 2018 |
| Crescendo Event Communication Limited | Other services | 2003 |
| Crescendo Events Limited | Professional & scientific | 2016 |
| Crescent Accounting Ltd | Professional & scientific | 2026 |
| Crest & Acre Limited | Transport & logistics | 2025 |
| Crewcabins Property Ltd | Real estate | 2016 |
| Cricketneverstops Limited | Wholesale & retail | 2025 |
| Critical Care Transfer Limited | Health & social care | 2022 |
| Croftworks Ltd | Manufacturing | 2018 |
| Crossfit Heathrow Ltd | Arts & recreation | 2019 |
| Crown Class Chauffeurs Ltd | Transport & logistics | 2025 |
| Crown Roofing & Leadwork Limited | Construction | 2025 |
| CRS Commercial Management Limited | Professional & scientific | 2014 |
| Crunchy Craves Limited | Hospitality | 2025 |
| CS Global Group Limited | Administrative & support | 2019 |
| Csls Couriers Ltd | Transport & logistics | 2020 |
| Csrp Ltd | Professional & scientific | 2024 |
| CSV9 Limited | Professional & scientific | 2018 |
| CTS International Logistics (UK) Co Ltd | Transport & logistics | 2021 |
| Curly Notch Ltd | Construction | 2026 |
| CUT Scenic Limited | Construction | 2018 |
| Cuzzpro Ltd | Information & communication | 2025 |
| Cuzztec Ltd | Construction | 2026 |
| Cyberguru Limited | Information & communication | 2017 |
| D & a Collection Ltd | Wholesale & retail | 2025 |
| D & J Rubbish Removal Limited | Water & waste | 2014 |
| D Parker Heating and Plumbing Ltd | Administrative & support | 2015 |
| D&A Driving Limited | Education | 2023 |
| D&A Properties & Investments Ltd | Households | 2019 |
| D.E.S. Management Services Limited | Professional & scientific | 1995 |
| D.L.F Heating Specialists Ltd | Construction | 2017 |
| Dabster Systems UK Limited | Information & communication | 2007 |
| Dahiya Logistics Limited | Professional & scientific | 2013 |