| Community of Christ in London Ltd | Other services | 1993 |
| Community Works 4U CIC | Education | 2014 |
| Communova Limited | Administrative & support | 2024 |
| Compaq Solutions Limited | Construction | 2014 |
| Compas Group Limited | Administrative & support | 2015 |
| Compassiq Ltd | Information & communication | 2025 |
| Complete Combustion Limited | Manufacturing | 2000 |
| Complete Control Services London Limited | Manufacturing | 2012 |
| Complete Roofing & Refurbishment Limited | Construction | 2023 |
| Completely Sound Limited | Professional & scientific | 2018 |
| Computair Holdings Limited | Financial services | 2023 |
| Computair Limited | Information & communication | 1980 |
| Compute Solutions Ltd | Information & communication | 2022 |
| Comtell Limited | Information & communication | 2017 |
| Comway Investments Limited | Administrative & support | 1988 |
| CON Does Car Stuff Ltd | Information & communication | 2025 |
| Conation Partners Limited | Health & social care | 2007 |
| Conbuild Management and Services Ltd | Construction | 2017 |
| Conepoint Limited | Hospitality | 2000 |
| Conlin Limited | Administrative & support | 2017 |
| Connect 4 Electrical Services Ltd | Construction | 2018 |
| Connect 5 Limited | Real estate | 2020 |
| Connect Locums Ltd | Administrative & support | 2019 |
| Connect Outsource Ltd | Administrative & support | 2023 |
| Connectmor Holdings Ltd | Financial services | 2025 |
| Constancia Ltd | Health & social care | 2014 |
| Construction Employment Services Limited | Construction | 2013 |
| Construction for Generations Limited | Construction | 2022 |
| Constructionrecruitment.Com Limited | Administrative & support | 2001 |
| Constructions a+ Ltd | Construction | 2021 |
| Consulenza Aquila Limited | Professional & scientific | 2024 |
| Consulo Advisors Ltd | Real estate | 2020 |
| Consultancy a+ Limited | Professional & scientific | 2017 |
| Contactum Limited | Manufacturing | 2009 |
| Contagious Bible Ministries | Education | 2011 |
| Continental Coaches Ltd | Transport & logistics | 2025 |
| Contrast London Ltd | Manufacturing | 2015 |
| Control Design Management Ltd | Information & communication | 2018 |
| Control Technologies UK Ltd | Information & communication | 2012 |
| Convenient PT Ltd | Arts & recreation | 2021 |
| Convert Your Space Limited | Construction | 2013 |
| Conway Haulage Limited | Transport & logistics | 2016 |
| Cook & Butler (Trading) Limited | Wholesale & retail | 2025 |
| Cook & Sons Property Limited | Hospitality | 2024 |
| Cook Trinity Limited | Construction | 2026 |
| Cookie Connoisseur Ltd | Manufacturing | 2024 |
| Cooks Cars Limited | Transport & logistics | 2024 |
| Cool Media Solutions Ltd | Information & communication | 2009 |
| Cool Solutions Engineering Limited | Construction | 2024 |
| Cooper Media Peterborough Ltd | Professional & scientific | 2025 |
| Cooper Shuttleworth Limited | Real estate | 1965 |
| Copper House Holdings Limited | Real estate | 2007 |
| Copperhouse Limited | Manufacturing | 2016 |
| Coppersmith Recruitment and Services Ltd | Administrative & support | 2015 |
| Corak Moments Ltd | Professional & scientific | 2024 |
| Corak Services Limited | Manufacturing | 2022 |
| Coralis Serv Ltd | Transport & logistics | 2017 |
| Core Amenity Ltd | Wholesale & retail | 2013 |
| Core Automation Limited | Professional & scientific | 2008 |
| Core Hire Staffing Ltd | Administrative & support | 2026 |
| Corebuild Solution Ltd | Construction | 2024 |
| Corner Barbers DUNSTABLE1 Ltd | Other services | 2025 |
| Corner Hall (Harpenden) Management Co Ltd | Households | 2019 |
| Cornish Ventures Ltd | Hospitality | 2016 |
| Cornwall Plumbing & Heating Services Ltd | Construction | 2023 |
| Corporate Events Plus Limited | Other services | 1998 |
| Corporate Security Limited | Administrative & support | 2022 |
| Corrective Farriery Limited | Agriculture & fishing | 2025 |
| Cosmetier Ltd | Health & social care | 2016 |
| Cosmo Food Limited | Hospitality | 2017 |
| Costcutter Birtley Limited | Wholesale & retail | 2016 |
| Costin Contractors Ltd | Construction | 2019 |
| Costy Drive Ltd | Transport & logistics | 2022 |
| Cosy Stays Direct Ltd | Real estate | 2024 |
| Cotswolds Property Developments Ltd | Construction | 2026 |
| Cougar (Midlands) Ltd | Construction | 2012 |
| Country House Pets Limited | Other services | 2023 |
| Country Spaces Limited | Hospitality | 2018 |
| Countrystays Property Group Ltd | Hospitality | 2026 |
| Countrystays Residential Limited | Real estate | 2023 |
| County Analytics Ltd | Information & communication | 2013 |
| County Flight Services Ltd | Transport & logistics | 2021 |
| Cove & Clay Ltd | Hospitality | 2025 |
| Covenant Homes Solution Ltd | Real estate | 2018 |
| Coventon Limited | Hospitality | 2024 |
| COX K9 Ltd | Administrative & support | 2022 |
| CPB Holdings Limited | Financial services | 2022 |
| CPD Quality Ltd | Education | 2022 |
| Craft Cart Ltd | Wholesale & retail | 2021 |
| Craftline Projects Limited | Manufacturing | 2021 |
| Craig Basham Heating and Plumbing Limited | Construction | 2011 |
| Craig Cowley Consultancy Ltd | Professional & scientific | 2025 |
| Craig Ringsell Sports Pitches Ltd | Arts & recreation | 2026 |
| CRE Builders Ltd | Construction | 2022 |
| Creabomb Ltd | Transport & logistics | 2013 |
| Create Construct Limited | Construction | 2015 |
| Creations Barbering Limited | Other services | 2019 |
| Creations Hairdressing Limited | Other services | 2012 |
| Creative Buffer Ltd | Arts & recreation | 2022 |
| Creative Draping Academy Ltd | Education | 2016 |