| Commercial Awnings Limited | Manufacturing | 2016 |
| Commercial Heat Pump Services Ltd | Construction | 2023 |
| Commercial Industrial Consctruction UK Limited | Manufacturing | 2017 |
| Commercial Property Warehouse Ltd | Real estate | 2013 |
| Common Dog Ltd | Professional & scientific | 2023 |
| Common Electrics Limited | Construction | 2021 |
| Common Ground Hospitality Ltd | Hospitality | 2026 |
| Comms Design Solutions Limited | Information & communication | 2015 |
| Community Access Network Limited | Health & social care | 1990 |
| Community Radio Swindon Limited | Information & communication | 2006 |
| Community Vision Group | Professional & scientific | 2021 |
| Community Witnesses CIC | Hospitality | 2025 |
| Company X Consulting Ltd | Information & communication | 2013 |
| Company X Consulting Services Ltd | Information & communication | 2017 |
| Compare Airport Parking Extras Limited | Other services | 2024 |
| Compass Energy Limited | Wholesale & retail | 2018 |
| Compass Technical Services Ltd | Professional & scientific | 2023 |
| Complete Accounting & Payroll (Swindon) Limited | Professional & scientific | 2013 |
| Complete Aquatics Limited | Administrative & support | 2016 |
| Complete Business Gifts Limited | Professional & scientific | 2002 |
| Complete Care 24 Limited | Health & social care | 2015 |
| Complete Fencing Solutions Ltd | Construction | 2022 |
| Complete Roofing and Building Services Ltd | Construction | 2022 |
| Complete Storage and Interiors Limited | Wholesale & retail | 2024 |
| Complete Sunshine Property Ltd | Real estate | 2022 |
| Complete Towbars Ltd | Manufacturing | 2012 |
| Compliance Systems Limited | Information & communication | 2011 |
| Complilet Ltd | Real estate | 2026 |
| Compton Aggregates Limited | Extraterritorial | 1978 |
| Computer Power Protection (Sales) Limited | Wholesale & retail | 2010 |
| Computeriotsupport Ltd | Information & communication | 2026 |
| Comsept Ltd | Arts & recreation | 2025 |
| Comwood Limited | Construction | 2023 |
| Conair Ltd | Construction | 2025 |
| Concept UK Limited | Construction | 1990 |
| Concepts Tattoo Limited | Other services | 2025 |
| Conceptual Furniture Ltd | Manufacturing | 2018 |
| Concerts at Sea Limited | Extraterritorial | 2012 |
| Concorde Cafe Ltd | Hospitality | 2019 |
| Confederation Mortgage Services Limited | Financial services | 1984 |
| Confederation of Paper Industries Limited | Other services | 1999 |
| Confuso Ltd | Wholesale & retail | 2025 |
| Conlon Employee Ownership Trustee Limited | Professional & scientific | 2024 |
| Conlon Limited | Construction | 2000 |
| Conlon Plant Limited | Administrative & support | 1999 |
| Connect Limited | Professional & scientific | 1986 |
| Connect Logistics Limited | Professional & scientific | 2014 |
| Connect News & Media Limited | Professional & scientific | 2013 |
| Connect Parcel Freight Limited | Professional & scientific | 2014 |
| Connect Parcels Limited | Professional & scientific | 2014 |
| Connect Services Limited | Professional & scientific | 2013 |
| Connect Specialist Distribution Group Limited | Professional & scientific | 2013 |
| CONNECT1ST Ltd | Information & communication | 2022 |
| CONNECT2U Limited | Professional & scientific | 2000 |
| Connies Chinese Take Away Limited | Hospitality | 2017 |
| Consilio International Limited | Professional & scientific | 2023 |
| Constant-In Services Ltd | Transport & logistics | 2017 |
| Constitution Hill Store PVT Ltd | Wholesale & retail | 2026 |
| Constructiondocs Ltd | Administrative & support | 2022 |
| Constructsure Ltd | Construction | 2010 |
| Consult Clearly Homes Limited | Real estate | 2018 |
| Consult Clearly Limited | Wholesale & retail | 2016 |
| Consulting LAB Ltd | Professional & scientific | 2021 |
| Consulting Structural Engineers G&J Group Ltd | Professional & scientific | 2018 |
| Consumables Corporate Group Limited | Wholesale & retail | 2009 |
| Consumables Manufacturing Limited | Wholesale & retail | 2009 |
| Consumables MBO II Limited | Financial services | 2024 |
| Consumables MBO Limited | Financial services | 2023 |
| Consumables Solutions Limited | Wholesale & retail | 1993 |
| Consumables Technology Limited | Information & communication | 2020 |
| Contagious Media Ltd | Information & communication | 2011 |
| Continental & China Investment Limited | Professional & scientific | 2003 |
| Continental Furniture Components Limited | Wholesale & retail | 1982 |
| Continuity of Care Ltd | Health & social care | 2025 |
| Contour Couture Ltd | Other services | 2019 |
| Contractual Insight Ltd | Professional & scientific | 2020 |
| Control Transportes Ltd | Transport & logistics | 2021 |
| Converged Networks Ltd | Information & communication | 2015 |
| Convey Technology Limited | Information & communication | 2016 |
| Conveyancing Data Services Ltd | Information & communication | 2010 |
| Cook & Marsh Decorating Limited | Construction | 1995 |
| Cookaracha Ltd | Hospitality | 2022 |
| Cookham Road 1965 Limited | Extraterritorial | 2014 |
| Cookie GOD Ltd | Hospitality | 2025 |
| Cool Running Campers & Construction Ltd | Wholesale & retail | 2022 |
| Cool Surface Limited | Arts & recreation | 2008 |
| Coolteq Ltd | Construction | 2024 |
| Coombe Housing Limited | Real estate | 2025 |
| Cooper Digital Assets Ltd | Other services | 2024 |
| Coorway Limited | Hospitality | 2022 |
| Cope Solutions Ltd | Wholesale & retail | 2025 |
| Copernicus Fire & Security Ltd | Administrative & support | 2025 |
| Copper Beeches Management Co. (Highworth) Limited(The) | Households | 1983 |
| Copse Avenue Management Company Limited | Households | 1982 |
| Copy Color Limited | Manufacturing | 2003 |
| Cora Healthcare Limited | Health & social care | 2018 |
| Coral Zoom Limited | Administrative & support | 2023 |
| Corbel Properties Limited | Construction | 2004 |
| Corda Construction Ltd | Construction | 2019 |
| Cordayla Marketing Limited | Professional & scientific | 2004 |