| City Brickwork (UK) Limited | Construction | 2003 |
| City Clinical Psychology Ltd | Health & social care | 2019 |
| City Hand Therapy Limited | Health & social care | 2017 |
| City Kegs Ltd | Administrative & support | 2019 |
| City Mastic & Fire (UK) Ltd | Construction | 2019 |
| CJ New Homes 2 Limited | Real estate | 2019 |
| CJ New Homes Limited | Real estate | 2019 |
| CJ Rogers Limited | Other services | 2019 |
| CJC Aviation Ltd | Wholesale & retail | 2019 |
| CJK Electrical (UK) Limited | Construction | 2007 |
| Cjms Consulting Ltd | Information & communication | 2007 |
| CJR Consulting International Limited | Professional & scientific | 2025 |
| CJS Carpentry Limited | Construction | 2015 |
| Claddagh Cabs Ltd | Transport & logistics | 2022 |
| Claddagh Homes Ltd | Real estate | 2022 |
| Clare Kneeshaw Limited | Information & communication | 2007 |
| Claret & Blue Photography Ltd | Professional & scientific | 2016 |
| Clarke Electrical Contractors Limited | Administrative & support | 2016 |
| Clifford & Evans Limited | Wholesale & retail | 2021 |
| Climatech Environmental Ltd | Construction | 2025 |
| Climbpass Ltd | Information & communication | 2026 |
| Clinnect Ltd | Other services | 2023 |
| Cloud Application Inc Ltd | Wholesale & retail | 2016 |
| CM Vending Ltd | Wholesale & retail | 2021 |
| CNP Solutions Limited | Information & communication | 2008 |
| COB Construction Limited | Construction | 2020 |
| Code Cutter Limited | Information & communication | 2013 |
| Codesigners Ltd | Administrative & support | 2017 |
| Cold Christmas Waste Management Limited | Other services | 2025 |
| Cole Green Recovery Limited | Transport & logistics | 2020 |
| Colin James Interiors Ltd | Construction | 2013 |
| Collins Coaches Limited | Transport & logistics | 2024 |
| Colourways Limited | Administrative & support | 1997 |
| Commercial Talent Payments Ltd | Administrative & support | 2022 |
| Communitel Limited | Information & communication | 1989 |
| Community Alliance Broxbourne and East Herts | Health & social care | 2007 |
| Community Energy Scheme Stoke Limited | Energy | 2018 |
| Community Energy Scheme UK Limited | Energy | 2017 |
| Compy Ltd | Administrative & support | 2026 |
| Conker Enterprises Limited | Arts & recreation | 2023 |
| Consener Ltd | Information & communication | 2014 |
| Contractors Design (CDS) Limited | Professional & scientific | 2020 |
| Contractors Design EOT Limited | Administrative & support | 2025 |
| Contractors Design Services Limited | Real estate | 2004 |
| Cool Cooks Catering Company Limited | Hospitality | 2005 |
| Cooloola Limited | Professional & scientific | 2012 |
| Cope & Cabrera Limited | Arts & recreation | 2015 |
| Copues Construction Limited | Construction | 2011 |
| Copues Properties Ltd | Real estate | 2016 |
| Coral Mechanical Ltd | Professional & scientific | 2025 |
| Coraldale Limited | Professional & scientific | 1999 |
| Corespace Interiors Ltd | Construction | 2026 |
| Corham Capital LLP | | 2007 |
| Corinne Rowlands Limited | Health & social care | 2025 |
| Corkisle Limited | Real estate | 1986 |
| Cornelis Consulting Limited | Professional & scientific | 2020 |
| Cosec-On-Demand Limited | Extraterritorial | 2024 |
| Cosmos Homes Limited | Professional & scientific | 2021 |
| Cotech Engineering Limited | Professional & scientific | 1991 |
| Coursebookers Limited | Information & communication | 2003 |
| Courtenays Properties Ltd | Construction | 2021 |
| Courtlands Skip Hire (UK) Limited | Extraterritorial | 2009 |
| Couture Consultancy Ltd | Professional & scientific | 2020 |
| CPB Lettings Limited | Real estate | 2026 |
| CR CAD Solutions Ltd | Construction | 2019 |
| Craftport Limited | Extraterritorial | 2013 |
| Crates of Wool Limited | Wholesale & retail | 2017 |
| Crates of Wool Training & Services Limited | Arts & recreation | 2018 |
| Creative Agents LP | | 2020 |
| Crep World Order Ltd | Wholesale & retail | 2024 |
| Cresthaven Construction Limited | Construction | 2012 |
| Cribbar Leasing Limited | Professional & scientific | 2023 |
| Croft Irrigation Ltd | Construction | 2023 |
| Croftson Property Ltd | Real estate | 2019 |
| Cromwell Road (Ware) Limited | Real estate | 1999 |
| Crown & Falcon Public House Ltd | Hospitality | 2019 |
| Crownstone Accountants Ltd | Professional & scientific | 2026 |
| Crownwide 2 Limited | Real estate | 2021 |
| Crownwide Investments Limited | Real estate | 2005 |
| Crownwide Limited | Real estate | 2014 |
| Crownwide Management Limited | Real estate | 2023 |
| Crownwide Properties LLP | | 2018 |
| Crystal Management Ltd | Real estate | 2023 |
| CSC Education Ltd | Professional & scientific | 2004 |
| Culture Catalyst Community Interest Company | Administrative & support | 2020 |
| Cupaz Herts Limited | Real estate | 2007 |
| Cupaz Ltd | Extraterritorial | 2007 |
| Cupaz Management LLP | | 2015 |
| Cura Vita Complex Care Group Limited | Health & social care | 2024 |
| Cura Vita Staffing Solutions Ltd | Administrative & support | 2025 |
| Curious Giraffes Ltd | Professional & scientific | 2017 |
| Curry Paradise Limited | Hospitality | 2024 |
| Cwomap Ltd | Education | 2020 |
| CX Blueprints Ltd | Information & communication | 2025 |
| Cyrene Ltd | Education | 2025 |
| D a Home Maintenance Limited | Construction | 2011 |
| D Bonner & Sons Ltd | Wholesale & retail | 2013 |
| D Q Ductwork UK Ltd | Construction | 2018 |
| D T Cardboard, Plastic and Pallets Recycling Limited | Wholesale & retail | 2025 |
| D Tomblin Treeworks Contracting Limited | Administrative & support | 2020 |