| Complypro Limited | Construction | 2025 |
| Complytrace Limited | Information & communication | 2026 |
| Composite Panel Structures UK Limited | Construction | 2024 |
| Compres Construction Ltd | Construction | 2023 |
| COMPUTING4KIDS Limited | Education | 2020 |
| Comtech E & I Limited | Extraterritorial | 2019 |
| CON Todo Limited | Hospitality | 2026 |
| Cona Mechanical Ltd | Professional & scientific | 2026 |
| Concept Accountancy Limited | Professional & scientific | 2012 |
| Concept Camden Audiology Ltd | Health & social care | 2025 |
| Concept Camden CL Ltd | Wholesale & retail | 2024 |
| Concept Coffee Works Ltd | Wholesale & retail | 2024 |
| Concept Crafters Limited | Wholesale & retail | 2024 |
| Concept Curate Holdings Limited | Information & communication | 2026 |
| Concept Curate Limited | Information & communication | 2025 |
| Concept EYE Clinic Limited | Wholesale & retail | 2005 |
| Concept Eyes Edinburgh Limited | Wholesale & retail | 2023 |
| Conceptual Developments Ltd | Construction | 2021 |
| Conciergo Limited | Administrative & support | 2024 |
| Concurrent PVT Ltd | Administrative & support | 2017 |
| Condensation Control (NE) Ltd | Professional & scientific | 2023 |
| Conex Data Systems Limited | Information & communication | 2010 |
| Conference of Socialist Economists | Manufacturing | 2004 |
| Confidence Wills Limited | Professional & scientific | 2018 |
| Coniscliffe Park Residents Management Company Limited | Real estate | 2025 |
| Conker Tech Ltd | Information & communication | 2024 |
| Connaught Associates Ltd | Professional & scientific | 2018 |
| Conndev Ltd | Information & communication | 2020 |
| Connect A30/A35 Holdings Limited | Professional & scientific | 2011 |
| Connect A30/A35 Limited | Construction | 1995 |
| Connect A50 Limited | Construction | 1995 |
| Connect Commerce Ltd | Wholesale & retail | 2026 |
| Connect Insolvency Limited | Professional & scientific | 2017 |
| Connect M1-A1 Holdings Limited | Construction | 1995 |
| Connect M1-A1 Limited | Construction | 1994 |
| Connect M77/GSO Holdings Limited | Professional & scientific | 2003 |
| Connect M77/GSO PLC | Construction | 2003 |
| Connect Roads Derby Holdings Limited | Professional & scientific | 2006 |
| Connect Roads Derby Limited | Administrative & support | 2006 |
| Connect Roads Infrastructure Investments Limited | Professional & scientific | 2010 |
| Connect Roads Limited | Professional & scientific | 1994 |
| Connected Energy Ltd | Manufacturing | 2010 |
| Connected Futures (Estates) Ltd | Real estate | 2026 |
| Connected Futures (Housing) Ltd | Hospitality | 2026 |
| Connected Futures (Resources) Ltd | Administrative & support | 2026 |
| Connected Futures Group Ltd | Financial services | 2026 |
| Connected Holdings Ltd | Financial services | 2018 |
| Connected Intelligence Ltd | Information & communication | 2025 |
| Connected Living London (Arnos Grove) Limited | Construction | 2019 |
| Connected Living London (Bollo Lane) Limited | Construction | 2024 |
| Connected Living London (BTR) Limited | Real estate | 2019 |
| Connected Living London (Cockfosters) Limited | Construction | 2019 |
| Connected Living London (Limmo) Limited | Construction | 2019 |
| Connected Living London (Montford Place) Limited | Construction | 2019 |
| Connected Living London (Nine Elms) Limited | Construction | 2019 |
| Connected Living London (Opco) Limited | Construction | 2019 |
| Connected Living London (RP) Limited | Real estate | 2019 |
| Connected Living London (Southall) Limited | Construction | 2019 |
| Connected Living London (Woolwich) Limited | Construction | 2019 |
| Connected Living London Ltd | Construction | 2012 |
| Connected Systems Consulting Limited | Information & communication | 2008 |
| Connected Voice | Other services | 2008 |
| Connexus Property Ltd | Real estate | 2015 |
| Connor and Graham Limited | Extraterritorial | 1955 |
| Connor Bailey Logistics Ltd | Transport & logistics | 2025 |
| Connor Fromson Property Investing Ltd | Real estate | 2025 |
| Cono Pizza Limited | Hospitality | 2019 |
| Conrad & Reuben Ltd | Wholesale & retail | 2015 |
| Conroy & Gill Properties Limited | Financial services | 2026 |
| Conroy Limited | Real estate | 2013 |
| Conscious Clubbing CIC | Other services | 2024 |
| Consett Cinemas Limited | | 1936 |
| Consett Property Partners LLP | | 2014 |
| Console Doctor Limited | Information & communication | 2008 |
| Consolidate Ltd | Information & communication | 2024 |
| Consolidated Shoe Corporation Limited | | 1920 |
| Consort Healthcare Infrastructure Investments Limited | Professional & scientific | 2009 |
| Constanta (NE) Ltd | Wholesale & retail | 2018 |
| Constantia Consult Limited | Professional & scientific | 2026 |
| Constantia Group Limited | Professional & scientific | 2026 |
| Construction & Management NE Limited | Professional & scientific | 2022 |
| Construction Cutting Services Limited | Manufacturing | 1987 |
| Construction&House Ltd | Construction | 2026 |
| Constructmasters Ltd | Construction | 2023 |
| Consult 48 Limited | Professional & scientific | 2022 |
| Consult Elorm Limited | Education | 2025 |
| Consult North Limited | Professional & scientific | 2020 |
| Consult Services North East Limited | Construction | 2025 |
| Consult-Ium Ltd | Professional & scientific | 2024 |
| Consultancy Direct UK Limited | Professional & scientific | 2014 |
| Consultant EYE Surgeons Partnership (North East) LLP | | 2006 |
| Consulting First Ltd | Transport & logistics | 2017 |
| Containment Collective Ltd | Professional & scientific | 2024 |
| Contec IAS UK Limited | Professional & scientific | 2018 |
| Content by the Sea Ltd | Professional & scientific | 2020 |
| Contentifai Ltd | Professional & scientific | 2023 |
| Contentqualityuk Ltd | Professional & scientific | 2024 |
| Contents Interior and Graphic Design Ltd | Professional & scientific | 2012 |
| Continental Contracting Limited | Administrative & support | 1993 |
| Continental L66 Huca and Logistics Ltd | Hospitality | 2025 |