| Cimar Properties Limited | Real estate | 2021 |
| Cimorge Ltd | Health & social care | 2025 |
| Cinar MK Ltd | Professional & scientific | 2024 |
| Cindev UK Limited | Financial services | 2018 |
| Cinebolic Ltd | Information & communication | 2025 |
| Cinehd Ltd | Information & communication | 2007 |
| Cinemaeyes Limited | Professional & scientific | 2015 |
| Cinescape Limited | Professional & scientific | 2024 |
| Cinnabar Consulting Limited | Health & social care | 2018 |
| Cinnamon Digital Applications Limited | Information & communication | 2018 |
| Cinoti Limited | Hospitality | 2015 |
| Cinq IT Limited | Information & communication | 2021 |
| Ciporet UK Limited | Real estate | 2023 |
| CIPRIANHGVDRIVERTRANSPORT1 Limited | Transport & logistics | 2021 |
| Ciqo Limited | Extraterritorial | 2011 |
| Circle of Vigour Ltd | Other services | 2024 |
| Circle Relocations Ltd | Households | 2019 |
| Circle Takes Limited | Information & communication | 2023 |
| Circuit Central Ltd | Wholesale & retail | 2025 |
| Circus Afterlife Ltd | Wholesale & retail | 2025 |
| Cirronix Digital Ltd | Wholesale & retail | 2026 |
| Cirrus Selection Limited | Administrative & support | 2017 |
| Ciscore Limited | Wholesale & retail | 2014 |
| Cissykims Limited | Health & social care | 2022 |
| Cistec Ltd | Professional & scientific | 2011 |
| Citadel 75 Ltd | Professional & scientific | 2025 |
| Citadel Credo Limited | Real estate | 2016 |
| Citi Limited | Professional & scientific | 1993 |
| Citi Living Estates Limited | Real estate | 2015 |
| Citi PPM Experts Limited | Professional & scientific | 1996 |
| Citi Virtual Learning Limited | Professional & scientific | 2020 |
| Citibase Business Management Ltd | Real estate | 2018 |
| Cititron Management Limited | Construction | 2014 |
| Citizen Design Limited | Professional & scientific | 2012 |
| Citizen Spaces Ltd | Real estate | 2023 |
| Citizens Care Ltd | Health & social care | 2023 |
| Citrus Financial Ltd | Financial services | 2007 |
| Citrus Mist Limited | Professional & scientific | 2010 |
| City Auto Works Ltd | Wholesale & retail | 2022 |
| City Aviation Capital Limited | Financial services | 2024 |
| City Cabz Ltd | Transport & logistics | 2022 |
| City Camping Ltd | Hospitality | 2011 |
| City Connect MK Ltd | Transport & logistics | 2025 |
| City Country Coast Stays Limited | Hospitality | 2023 |
| City Discovery Centre | Education | 1987 |
| City Discovery Centre (Trading) Co. Limited | Education | 1997 |
| City Driving Limited | Education | 2025 |
| City Estates (MK) Limited | Construction | 2003 |
| City Fire Solutions Ltd | Professional & scientific | 2015 |
| City Garden 1 Ltd | Health & social care | 2020 |
| City Haircut Limited | Other services | 2014 |
| City Hand Car Wash & Valeting Ltd | Wholesale & retail | 2014 |
| City Interactive Spolka Akcyjna | | 2008 |
| City Investment Group Limited | Real estate | 2018 |
| City Investment Strategies | Financial services | 2017 |
| City Nails MK Limited | Other services | 2022 |
| City Pathway Limited | Professional & scientific | 2025 |
| City Plumbers Ltd | Construction | 2023 |
| City Root Management Ltd | Real estate | 2026 |
| City Smart Ltd | Real estate | 2018 |
| City Stay (MK) Ltd | Administrative & support | 2018 |
| City Stay Apartments Ltd | Real estate | 1993 |
| City Stay Investments Limited | Real estate | 2020 |
| City View Saffron Hill Limited | Households | 2013 |
| Cityarch Limited | Construction | 1975 |
| Cityflats Ltd | Real estate | 2023 |
| Citylite MK Ltd | Construction | 2023 |
| CITYTAXIS18 Ltd | Transport & logistics | 2019 |
| Ciupe Florin Limited | Administrative & support | 2017 |
| CIV Facades Ltd | Construction | 2019 |
| Civescomposites Ltd | Construction | 2025 |
| Civic Verifiers Ltd | Professional & scientific | 2026 |
| Civil Technology Limited | Construction | 2015 |
| CJ Aviation Safety Consultancy Limited | Professional & scientific | 2013 |
| CJ Fashions Limited | Arts & recreation | 2016 |
| CJ Home Properties Limited | Real estate | 2026 |
| CJ Machining Ltd | Wholesale & retail | 2025 |
| Cjda Holdings Limited | Information & communication | 2022 |
| CJE Educational Consultancy Limited | Education | 2025 |
| CJG Commercial Ltd | Professional & scientific | 2022 |
| CJN Controls Ltd | Construction | 2019 |
| CJP Public Relations Limited | Professional & scientific | 1993 |
| Cjrose Plumbing & Heating Ltd | Construction | 2023 |
| Cjrs Infosystems Limited | Information & communication | 2024 |
| CJT Coaching Ltd | Arts & recreation | 2023 |
| CJT Graphics Ltd | Administrative & support | 2020 |
| CK 2023 Limited | Administrative & support | 2023 |
| CK Management Limited | Health & social care | 2005 |
| CKS Integrated Care Services Ltd | Health & social care | 2024 |
| CKT Infotech Limited | Information & communication | 2025 |
| CL Gift Holdings Ltd | Wholesale & retail | 2014 |
| CL Haven Services Ltd | Health & social care | 2023 |
| Cl-Ear.Me Limited | Health & social care | 2024 |
| Clagio Ltd | Wholesale & retail | 2020 |
| Claims Portal Limited | Administrative & support | 2010 |
| Claire Dowling Case Management Ltd | Other services | 2025 |
| Claire Laveaux Ltd | Health & social care | 2025 |
| Clam Holdings Ltd | Financial services | 2022 |
| Clan & Cloth Ltd | Wholesale & retail | 2026 |
| Clare Court Management Company (Dunstable) Limited | Households | 1990 |