| City Haulage Limited | Administrative & support | 2007 |
| City News Network Limited | Information & communication | 2016 |
| City of Salvation International Ministries Ltd | Other services | 2019 |
| City Rides Northampton Limited | Transport & logistics | 2023 |
| Cityhill Estates Ltd | Real estate | 2018 |
| Cityline Travel Ltd | Transport & logistics | 2025 |
| Citylink Express Limited | Transport & logistics | 2018 |
| Citymobile Ltd | Wholesale & retail | 2020 |
| Civitas Security C.I.C. | Administrative & support | 2016 |
| Civon Limited | Real estate | 2019 |
| Ciwm Enterprises Ltd | Other services | 1992 |
| Ciwm International Limited | Administrative & support | 1998 |
| CJ EGO Services Limited | Health & social care | 2014 |
| CJ Holdings (Brixworth) Limited | Real estate | 2021 |
| CJ Leisure Holdings Ltd | Hospitality | 2022 |
| CJB Electrical Installations Ltd | Construction | 2014 |
| CJB Homes Ltd | Real estate | 2025 |
| CJC Blinds Limited | Construction | 2019 |
| CJD UK Holdings Limited | Financial services | 2024 |
| CJH Software Support Limited | Information & communication | 1988 |
| CJM Automotive Ltd | Other services | 2019 |
| Cjmac Associates Ltd | Transport & logistics | 2025 |
| Cjmolano Ltd | Administrative & support | 2022 |
| CJR Finishing Services Limited | Manufacturing | 2011 |
| CJR Midlands Group Limited | Professional & scientific | 2023 |
| CJR Special Projects Limited | Construction | 2023 |
| CJS Care (Northampton) Ltd | Extraterritorial | 2019 |
| CJS Leathers Limited | Wholesale & retail | 2015 |
| CJW Finance Limited | Financial services | 2010 |
| CK Automotive Limited | Professional & scientific | 2018 |
| CKN Logistics Limited | Transport & logistics | 2018 |
| CKN Print Limited | Manufacturing | 2002 |
| CKN Solutions Limited | Administrative & support | 2021 |
| CKO Intelligence Ltd | Information & communication | 2025 |
| CL Motorsport Ltd | Wholesale & retail | 2023 |
| CL6TG Farming Limited | Agriculture & fishing | 2021 |
| Cladding Maintenance & Solutions Limited | Construction | 2007 |
| Claire Berry Planning Limited | Professional & scientific | 2018 |
| Clairefish Limited | Health & social care | 2021 |
| Clairet Scientific Limited | Professional & scientific | 1994 |
| Clan Trading Ltd | Wholesale & retail | 2020 |
| Clancy Electrical Services Limited | Construction | 2023 |
| Clanrock Limited | Professional & scientific | 1992 |
| Clarah's House of Care Ltd | Health & social care | 2023 |
| Clarati Ltd | Information & communication | 2010 |
| Clare Pollard Ltd | Information & communication | 2021 |
| Clare Street Recording Studios Ltd | Information & communication | 2022 |
| Claremont Consulting Limited | Administrative & support | 2002 |
| Claremont Controls Limited | Information & communication | 1980 |
| Claremont Day Nursery Limited | Other services | 2000 |
| Clarence Cottages Ltd | Real estate | 2022 |
| Clarendon Construction & Design Ltd | Construction | 2020 |
| Clarendon Court (Rugby) Limited | Households | 1987 |
| Claret Control Limited | Households | 1992 |
| Clarges Transport Limited | Transport & logistics | 2025 |
| Clarice Holdings and Investments Ltd | Real estate | 2019 |
| Clarisent Limited | Information & communication | 2010 |
| Clarity Axis Limited | Construction | 2016 |
| Clark & John Financial Services Limited | Administrative & support | 2006 |
| Clark and Co Design Limited | Professional & scientific | 2025 |
| Clark Bird Consulting Ltd | Information & communication | 2019 |
| Clarke Consulting Ltd | Professional & scientific | 2002 |
| Clarke Event Solutions Limited | Information & communication | 2010 |
| Clarnor Estates Holdings Limited | Financial services | 2021 |
| Clarus Accountancy Group Limited | Professional & scientific | 2025 |
| Clas Plumbing Ltd | Construction | 2025 |
| Class One Recruitment Solutions Ltd | Professional & scientific | 2006 |
| Class Talent Ltd | Education | 2013 |
| Classic Parts for YOU Ltd | Wholesale & retail | 2022 |
| Classic Racad (UK) Ltd. | Professional & scientific | 2011 |
| Classic Racing Drivers Club Limited | Extraterritorial | 2010 |
| Classique Co. Trading Limited | Other services | 1996 |
| Classix Design & Developments Limited | Construction | 1976 |
| Classy Curves Ltd | Wholesale & retail | 2022 |
| Clau LUX Cleaning Ltd | Administrative & support | 2022 |
| CLAU3222 Ltd | Transport & logistics | 2022 |
| Claudio Ltd | Transport & logistics | 2019 |
| Claudiu Transport Solution Ltd | Transport & logistics | 2024 |
| Claudius Engineering Services Limited | Professional & scientific | 2010 |
| Claus Courier Ltd | Transport & logistics | 2019 |
| Clayclad U.K. Ltd | Construction | 2013 |
| Claypark Holdings Ltd | Real estate | 2024 |
| Clayson Country Homes Limited | Construction | 1987 |
| Clayson Linguistic Validation Services Ltd | Professional & scientific | 2017 |
| Clayson Loft Company Limited | Construction | 2000 |
| Clayson Property Developments Ltd | Real estate | 2026 |
| Clayson Property Limited | Real estate | 2014 |
| Clayson Rentals Limited | Real estate | 2016 |
| Clayson Windows Ltd | Construction | 2019 |
| Clayton Mills Ltd | Real estate | 2008 |
| CLC Lawyers Ltd | Professional & scientific | 2024 |
| CLC Logistics Ltd | Transport & logistics | 2025 |
| Clean Air Solutions LEV Ltd | Professional & scientific | 2020 |
| Clean and Gleam MK Limited | Other services | 2015 |
| Clean Care by Sharpeye Ltd | Other services | 2014 |
| Clean Coach Katie Limited | Administrative & support | 2016 |
| Clean Living Ltd | Administrative & support | 2025 |
| Clean That Productions Ltd | Administrative & support | 2011 |
| CLEAN4SHAW Ltd | Extraterritorial | 2023 |
| Cleanfleet Energy Group Limited | Energy | 2026 |