| Choruslane Limited | Households | 1985 |
| CHP Investments Limited | Real estate | 2016 |
| Chris Kerr Limited | Manufacturing | 2011 |
| Chris Lawson Associates Limited | Financial services | 2024 |
| Chris Plevin Ltd | Information & communication | 2022 |
| Christian Corner Limited | Health & social care | 2015 |
| Christmas Perks Limited | Wholesale & retail | 2019 |
| Chrome Linings Estates Ltd | Real estate | 2021 |
| Chucky Chicken Takeaway Ltd | Hospitality | 2015 |
| Church Green Properties Ltd | Real estate | 2017 |
| Chybr Ltd | Information & communication | 2026 |
| Cibco Limited | Real estate | 2004 |
| Cicu Catalin Limited | Construction | 2007 |
| Cinesteel Services Limited | Manufacturing | 2025 |
| Cinnabar Wharf RMC Limited | Households | 2016 |
| Circ-Hiit UK Ltd | Education | 2023 |
| Circuit Car Sales Limited | Wholesale & retail | 2013 |
| Cissyeze Ltd | Real estate | 2023 |
| City & County (2019) Limited | Construction | 1996 |
| City & County Limited | Construction | 1991 |
| City & Provincial (Equity Partners 3) Limited | Real estate | 2004 |
| City and Westminster Limited | Other services | 1982 |
| City Catering Rental Limited | Administrative & support | 2024 |
| City View Residents Management Company Limited | Households | 2010 |
| Citysound Limited | Construction | 2006 |
| Civic Square Ltd | Manufacturing | 2008 |
| Civilised Building Services Ltd | Construction | 2025 |
| Civitas Projects Ltd | Real estate | 2019 |
| Cjaz Ltd | Information & communication | 2014 |
| CJP Construction & Landscaping Ltd | Construction | 2022 |
| CJS Building Maintenance Limited | Construction | 2017 |
| CJS Electrical Installations Ltd | Construction | 2022 |
| CJW AV and Automation Ltd | Construction | 2017 |
| Ckft (Hampstead) LLP | | 2005 |
| Ckiffe Ltd | Construction | 2025 |
| Cksn Ltd | Wholesale & retail | 2013 |
| CL George Real Estate Limited | Real estate | 2020 |
| CL Luffy Real Estate Limited | Real estate | 2019 |
| Claire Anderton Limited | Arts & recreation | 2022 |
| Clam Prayer Academy UK | Other services | 2013 |
| Claremont Properties (Surbiton) | Real estate | 1960 |
| Clarence Court (Mill Hill) Management Company Limited | Households | 2007 |
| Clarence Gate Ltd | Construction | 2021 |
| Clarendon RTM Company Limited | Households | 2011 |
| Clarident Implant & Aesthetic Clinic Ltd | Financial services | 2026 |
| Clarity Homes Holdings Ltd | Financial services | 2020 |
| Classwork Property Services Ltd | Construction | 2014 |
| Claudia Health Care Ltd | Health & social care | 2019 |
| Claybury Management Limited | Households | 1967 |
| CLE Pharma Filling Limited | Professional & scientific | 2020 |
| Clean Energy & Renewable Technology Ltd | Construction | 2019 |
| Clean Paws Ltd | Manufacturing | 2022 |
| Clear Aesthetics by KP Ltd | Other services | 2019 |
| Clear Choice Automotive Ltd | Wholesale & retail | 2012 |
| Clear Company Services Limited | Professional & scientific | 2026 |
| Clearcut Insights Ltd | Professional & scientific | 2024 |
| Clearlake Cleaning Limited | Administrative & support | 2013 |
| Clemence Hoar Cummings Group Limited | Professional & scientific | 2023 |
| Clemence Hoar Cummings Limited | Professional & scientific | 2021 |
| Clermont Consultants (UK) Limited | Professional & scientific | 1997 |
| Clermont Directors Limited | Administrative & support | 2023 |
| Clermont Secretaries Limited | Administrative & support | 2023 |
| Clermont Trust (UK) Limited | Administrative & support | 2022 |
| Clermonte Services Limited | Professional & scientific | 2008 |
| Cleveland Court Freehold Management Ltd | Households | 2017 |
| Clews Construction Ltd | Information & communication | 2021 |
| Clifton Advisory Ltd | Professional & scientific | 2022 |
| Clim Performance Ltd | Construction | 2020 |
| Climate Engineers Limited | Construction | 2018 |
| Clinical Employment Services Ltd | Administrative & support | 2004 |
| Clippers N Snippers Limited | Other services | 2014 |
| Clique Property Ltd | Real estate | 2022 |
| Clisk Limited | Wholesale & retail | 2012 |
| Cliveden Foods Ltd | Wholesale & retail | 2023 |
| Cloisters Freehold Ltd | Extraterritorial | 2012 |
| Clontara Developments Limited | Construction | 2016 |
| Clontarf Holdings Ltd | Wholesale & retail | 2014 |
| Closeout Assured Ltd | Construction | 2025 |
| Closer Partners (Sussex) Ltd | Information & communication | 2018 |
| Closing Circles Limited | Professional & scientific | 2023 |
| Clota Varde Limited | Professional & scientific | 2022 |
| Cloud Beyond Ltd | Professional & scientific | 2014 |
| Cloud Concepts Solution Ltd | Information & communication | 2016 |
| Cloud Health Group Ltd | Health & social care | 2020 |
| Cloud Robot Ltd | Arts & recreation | 2026 |
| Cloudtoggle Limited | Information & communication | 2023 |
| Clovercourt (Dgmd) Ltd | Construction | 2026 |
| Clovercup | Real estate | 2001 |
| CLR Landscapes Limited | Administrative & support | 2018 |
| CLS 1ST Ltd | Wholesale & retail | 2020 |
| Club Excel Leisure Limited | Arts & recreation | 2010 |
| Clyde Moray Group Ltd | Professional & scientific | 2019 |
| Clyde Moray Ltd | Professional & scientific | 2019 |
| CM1 Global Ltd | Wholesale & retail | 2022 |
| CMB Stagehand Ltd | Construction | 2025 |
| CMD2021 Construction Ltd | Construction | 2021 |
| CML Sets Limited | Information & communication | 2011 |
| Cniguard Ltd | Manufacturing | 2005 |
| Coal Exchange Hotel LLP | | 2016 |
| Coban Weddings Ltd | Information & communication | 2018 |