| City Grey Limited | Construction | 2018 |
| City Grey Plant Limited | Administrative & support | 2023 |
| City Hawks Pest Management Limited | Administrative & support | 2020 |
| City Home Real Estate Ltd | Real estate | 2024 |
| City Lawyers (Personal Injury) Limited | Professional & scientific | 2009 |
| City of ST. Albans Swimming Coaches Limited | Arts & recreation | 2011 |
| City Point (ST Albans) RTM Company Limited | Households | 2026 |
| City Sporting Group Ltd | Arts & recreation | 2026 |
| City Surveying Limited | Administrative & support | 2023 |
| Civic Oakview Ltd | Households | 2024 |
| Civic Rose Garden Regeneration CIC | Administrative & support | 2024 |
| Civilised Solutions Ltd | Administrative & support | 2020 |
| CJ Monks Limited | Financial services | 2014 |
| CJ Tilbrook Advisory Limited | Professional & scientific | 2025 |
| CJT Advisory Limited | Professional & scientific | 2014 |
| CK & J Ltd | Information & communication | 2016 |
| CK Fruitful Limited | Real estate | 2025 |
| CKM Media Ltd | Professional & scientific | 2021 |
| Ckmv Ltd | Education | 2017 |
| CKS Watermain Solutions Limited | Water & waste | 2017 |
| CLA Design Ltd | Professional & scientific | 2020 |
| Claim Capital Litigation Partners LLP | | 2020 |
| Claims Audit Services Limited | Professional & scientific | 2023 |
| Clare Bartholdi Designs Ltd | Wholesale & retail | 2018 |
| Clare Court (ST Albans) Limited | Administrative & support | 2005 |
| Clare Rickard Design Ltd | Professional & scientific | 2018 |
| Claremont Property Services Ltd | Construction | 2024 |
| Clarence Commercial Consulting Ltd | Construction | 2024 |
| Clarence Events Ltd | Extraterritorial | 2019 |
| Clarence Lodge Nursery Ltd | Health & social care | 2022 |
| Clarence Mews (ST Albans) Management Company Limited | Households | 2001 |
| Clarence Park Mansions Limited | Households | 2002 |
| Clarence Park Mews Management Company Limited | Households | 2010 |
| Clarid Services Limited | Administrative & support | 2007 |
| Claritopia Ltd | Health & social care | 2022 |
| Clarity 11 Group Limited | Arts & recreation | 2015 |
| CLARITY360 Technologies Ltd | Information & communication | 2026 |
| Clark Systems Engineering Consulting Ltd | Professional & scientific | 2023 |
| Clarks Construction Group Limited | Construction | 2022 |
| Clarks Construction Limited | Construction | 2005 |
| Classics Castings Ltd | Manufacturing | 2025 |
| Claxton Solutions Limited | Real estate | 2013 |
| CLE Accounting Limited | Professional & scientific | 2019 |
| Cleamax Engineering Limited | Manufacturing | 2002 |
| Clean AZA Whistle Limited | Administrative & support | 2007 |
| Cleaning With Meaning Herts Limited | Administrative & support | 2024 |
| Clear Load Ltd | Water & waste | 2026 |
| Clear Sky Cleaning Ltd | Administrative & support | 2025 |
| Clear View Cleaning Contractors Ltd | Administrative & support | 2023 |
| Clear View Deionised Water & Cleaning Supplies Ltd | Administrative & support | 2024 |
| Clear View Home Improvements Development & Maintenance Ltd | Administrative & support | 2024 |
| Clearaway Asbestos Surveys Ltd | Professional & scientific | 2025 |
| Clearcut Edit Ltd | Information & communication | 2022 |
| Clearcut Production Ltd | Information & communication | 2013 |
| Clearwater Consult and Coach Limited | Administrative & support | 2022 |
| Clearway Gritting Limited | Administrative & support | 2010 |
| Clements Catering Ltd | Administrative & support | 2025 |
| Cleveland Lincoln Limited | Information & communication | 2013 |
| Cleveland Solutions Limited | Construction | 2026 |
| Clever Option Limited | Wholesale & retail | 2016 |
| Cleverton Ventures SPV 01 LLP | | 2021 |
| Cleverton Ventures SPV 02 LLP | | 2021 |
| Click Source Ltd | Professional & scientific | 2026 |
| Clico Capital Limited | Professional & scientific | 2007 |
| CLIMATE7 Limited | Professional & scientific | 2025 |
| Clinch Data Services Ltd | Professional & scientific | 2022 |
| Cline Consulting Limited | Information & communication | 2012 |
| Clinical Investments Limited | Financial services | 2023 |
| Clinpsy Limited | Health & social care | 2014 |
| Clockapub Limited | Information & communication | 2026 |
| Clogher Properties Ltd | Financial services | 2015 |
| Cloned Ltd | Manufacturing | 2022 |
| Cloud Comics Ltd | Wholesale & retail | 2020 |
| Cloudberry Consulting Limited | Professional & scientific | 2011 |
| Cloudview Ltd | Information & communication | 2014 |
| Club Kidz Limited | Health & social care | 2013 |
| Club Live Ltd | Extraterritorial | 2013 |
| Club Monarchy Ltd | Administrative & support | 2018 |
| Clutton Partners Limited | Professional & scientific | 2014 |
| Clydesdale Whetstone Limited | Households | 1996 |
| CM Physiotherapy Ltd | Health & social care | 2019 |
| CMA Development Limited | Construction | 2024 |
| CMC Investments Limited | Financial services | 2020 |
| Cmmc Investments Limited | Real estate | 2021 |
| CN Interiors Ltd | Construction | 2018 |
| CNC Investment Group Ltd | Real estate | 2023 |
| CNL Developments Limited | Professional & scientific | 2001 |
| Coach in the City Ltd | Professional & scientific | 2013 |
| Coached With Chloe Ltd | Health & social care | 2025 |
| Coachpath Ltd | Administrative & support | 2019 |
| Coastal Products Limited | Wholesale & retail | 2019 |
| Cobo Innovations Limited | Manufacturing | 2018 |
| Cobot Services Ltd | Information & communication | 2025 |
| Coccium Productions Limited | Information & communication | 2023 |
| Coda Transformation Limited | Professional & scientific | 2026 |
| Code Clarity Global Ltd | Professional & scientific | 2023 |
| Codreanu and Friends Ltd | Construction | 2025 |
| Coeliac Dietitian Ltd | Health & social care | 2023 |
| Coffee Filtered Limited | Information & communication | 2025 |
| Cogent Locum Limited | Wholesale & retail | 2023 |