| Collioure Ventures Ltd. | Financial services | 2017 |
| Colour Marketing Services Limited | Manufacturing | 2006 |
| Colour ME Social Limited | Professional & scientific | 2015 |
| Colour Print Direct Limited | Manufacturing | 2010 |
| Colour Soup Ltd | Construction | 2016 |
| Colourfast Group Limited | Administrative & support | 1990 |
| Colourworker Ltd | Information & communication | 2021 |
| Columbia Residential Limited | Professional & scientific | 2016 |
| Columns Design & Associates Limited | Households | 2004 |
| Colville Court (Eastbourne) Limited | Households | 1996 |
| Combicloud Ltd | Information & communication | 2014 |
| Combination Languages LLP | | 2017 |
| Commerce Way Management Company Limited | Real estate | 2005 |
| Commercial Clarity Limited | Professional & scientific | 2014 |
| Commercial Finance South East Limited | Professional & scientific | 2017 |
| Commercial GAS and Boiler Services Ltd | Construction | 2019 |
| Commercial Impact Limited | Professional & scientific | 2023 |
| Commglass Ltd | Construction | 2015 |
| Commonwealth Entertainment Ltd | Wholesale & retail | 2026 |
| Communication IS Limited | Professional & scientific | 2007 |
| Communications Advisory Service Limited | Information & communication | 2005 |
| Communikate Design Limited | Professional & scientific | 2023 |
| Communitas Public Relations Ltd | Professional & scientific | 1994 |
| Communitee App Ltd | Professional & scientific | 2024 |
| Community Beauty Limited | Other services | 2024 |
| Community Counselling Brighton C.I.C. | Health & social care | 2024 |
| Community Together Communications Ltd | Information & communication | 2006 |
| Community Transport B&H (Trading) Limited | Transport & logistics | 2002 |
| Community Works Consultancy Limited | Professional & scientific | 2015 |
| COMO1907 Limited | Real estate | 2019 |
| COMP3 Ltd | Information & communication | 2025 |
| Compacta-Bin Limited | Extraterritorial | 1999 |
| Compass Heating Services Limited | Professional & scientific | 2020 |
| Compass International Ltd | Information & communication | 2019 |
| Compayne (Hampstead) Limited | Construction | 1955 |
| Compensation Marketing Associates Limited | Information & communication | 2014 |
| Complete Cleaning Group Ltd | Administrative & support | 2022 |
| Complete Control (2020) Ltd | Extraterritorial | 2020 |
| Complete Fone Solutions Limited | Wholesale & retail | 2015 |
| Complete Workforce Solutions Ltd | Administrative & support | 2018 |
| Complianceassist Limited | Administrative & support | 2009 |
| Comply OR DIE Ltd | Professional & scientific | 2020 |
| Composable Consulting Ltd | Information & communication | 2025 |
| Compton Property Holdings London Limited | Real estate | 2025 |
| Computer Eyez (South) Ltd | Information & communication | 2006 |
| Computer Generated Limited | Professional & scientific | 2019 |
| Computer Systems Engineers Ltd | Information & communication | 2013 |
| Comstruct Ltd | Construction | 2014 |
| Comware Labs Limited | Information & communication | 2013 |
| Concept Audio Limited | Arts & recreation | 2005 |
| Concepts Group Holdings Limited | Financial services | 2022 |
| Conch Clothing Limited | Manufacturing | 2015 |
| Conclave Brighton Ltd | Construction | 2018 |
| Concorbit Ltd | Information & communication | 2026 |
| Concorde Education Services Ltd | Other services | 2016 |
| Condor Technology Services Limited | Information & communication | 2025 |
| Conduit Productions Limited | Information & communication | 2024 |
| Conformity Software Limited | Information & communication | 2021 |
| Conicol Limited | Real estate | 1978 |
| Coniston Court (North) Hove Limited | Households | 2004 |
| Connect Design Ltd | Professional & scientific | 2020 |
| CONNECT2COUNSELLORS Limited | Information & communication | 2015 |
| Connected Brighton Ltd | Professional & scientific | 2021 |
| Connected Consumers Ltd | Professional & scientific | 2023 |
| Connecting Development Ltd | Professional & scientific | 2020 |
| Connecting on Purpose Limited | Professional & scientific | 2013 |
| Connection Clinic Ltd | Health & social care | 2026 |
| Connections UK Brighton Ltd | Transport & logistics | 2011 |
| Connor Capital Ventures Limited | Real estate | 2024 |
| Conrye Carpentry Ltd | Construction | 2019 |
| Conscious Business People Ltd | Professional & scientific | 2009 |
| Conscious Capital Coaching Ltd | Professional & scientific | 2023 |
| Conscious Holdings Limited | Financial services | 2024 |
| Consec Limited | Other services | 2020 |
| Conservatory Events Ltd | Hospitality | 2019 |
| Conserve Building Services Ltd | Construction | 2010 |
| Considered Works Ltd | Professional & scientific | 2023 |
| Considine Limited | Professional & scientific | 2009 |
| Consist Creative Consultancy Ltd | Professional & scientific | 2024 |
| Constable Landscaping Ltd | Construction | 2010 |
| Constance Partners Limited | Professional & scientific | 2018 |
| Constant Consulting Limited | Professional & scientific | 2008 |
| Constant Heating Supplies Limited | Construction | 2015 |
| Constantinople Bistro Ltd | Hospitality | 2017 |
| Constantinople Food Ltd | Hospitality | 2019 |
| Construction Cleaning Solutions Ltd | Administrative & support | 2026 |
| Construction Portal Limited | Construction | 2018 |
| Construction Technologies & Innovation Ltd | Construction | 2019 |
| Construction Visuals Ltd | Construction | 2026 |
| Consult Media Ltd | Other services | 2022 |
| Consulting Wholesale Ltd | Wholesale & retail | 2018 |
| Consultwiz Ltd | Information & communication | 2022 |
| Contactless Travel Ltd | Professional & scientific | 2019 |
| Contain Yourself Storage Limited | Administrative & support | 2018 |
| Containment Records Ltd | Information & communication | 2012 |
| Context and Intent Limited | Information & communication | 2023 |
| Contextflow Limited | Information & communication | 2024 |
| Continuous Play Holdings Ltd | Financial services | 2021 |
| Contrast One Limited | Professional & scientific | 2025 |
| Contraxo Ltd | Construction | 2018 |