| Convert Well Limited | London | 2024 |
| Coopertek Limited | Kirkwall | 2014 |
| Copper Bay (UK) Ltd | London | 2011 |
| Copper Bay Limited | London | 2010 |
| Copper Gold Resources Limited | London | 2005 |
| Copycat Pearl Limited | Brighton | 2022 |
| Coral Subsea Limited | Warrington | 2014 |
| Corby Limited | | 1996 |
| Corcel (Angola) Ltd | London | 2024 |
| Corcel (KON-11) Ltd | London | 2024 |
| Corcel (KON-12) Ltd | London | 2024 |
| Corcel (KON-16) Ltd | London | 2024 |
| Core Aggregates Ltd | Cookstown | 2013 |
| Core Laboratories (U.K.) Limited | London | 1994 |
| Core Natural Resources Europe Limited | London | 2011 |
| Core Specialist Services Limited | Aberdeen | 2010 |
| Corinth International Limited | Oxford | 2025 |
| Corlands Minerals Limited | North Yorkshire | 1962 |
| Cormin Limited | Thirsk | 2022 |
| Cornerstone North Sea Ltd | Bromley | 2020 |
| Cornish Battery Metals Limited | London | 2022 |
| Cornish Chamber of Mines and Minerals | Truro | 1917 |
| Cornish Holdings Ltd | Redruth | 2024 |
| Cornish Lithium G5 Limited | Cornwall | 2020 |
| Cornish Lithium Geothermal Limited | Cornwall | 2021 |
| Cornish Lithium Hard Rock Limited | Cornwall | 2021 |
| Cornish Lithium PLC | Penryn | 2016 |
| Cornish Metals Holdings Limited | Truro | 2016 |
| Cornish Metals PLC | Truro | 2025 |
| Cornish Minerals UK Limited | Truro | 2024 |
| Cornish Mining Company Ltd | Falmouth | 2021 |
| Cornish Sea Salt Company Limited | Helston | 2004 |
| Cornish TIN Limited | London | 2026 |
| Cornwall Mining Services Limited | St John | 2022 |
| Cornwall Resources Limited | London | 2012 |
| Cornwall TIN Limited | St. Ives | 2015 |
| Coro Europe Limited | Northolt | 2006 |
| Corporate Integrity Limited | Hawkhurst | 2009 |
| Corpro Systems Limited | Glasgow | 1988 |
| Corpus Resources PLC | London | 2016 |
| Correen Resources Ltd | Alford | 2013 |
| Corrichie Tech Ltd | Banchory | 2016 |
| Cortez Subsea Limited | Aberdeen | 2010 |
| Cosdos Limited | Aberdeen | 2026 |
| Cosl UK Limited | Aberdeen | 2022 |
| Cosmicsplash Ltd | Aberdeen | 2015 |
| Costwold Granite & Marble Ltd | Abingdon | 2017 |
| Cote D'Ivoire Japan Petroleum Limited | London | 2014 |
| Cotswold Hill Stone & Masonry Limited | Evesham | 2007 |
| Cotswold Natural Stone Limited | Nr Burford | 1996 |
| Cotswold Stone Quarries Limited | Worcestershire | 1989 |
| Cotswold Stone Supplies Limited | Tetbury | 1996 |
| Courage Energy (U.K.) Limited | Leigh-On-Sea | 1997 |
| Cousin DFS Ltd | Huddersfield | 2016 |
| Coutts Mining (UK) Ltd | London | 2019 |
| Cove Energy Limited | London | 2003 |
| Cove Farm Quarry Limited | Doncaster | 2014 |
| Covenant Resources Ltd | Cairndow | 2025 |
| Cover Global Ltd | Romford | 2026 |
| Cover Network UK Limited | Northolt | 2004 |
| Cowal Sand & Gravel Ltd. | Dunoon | 2004 |
| Coybndt Limited | Wallasey | 2016 |
| Cozilico UK Ltd | London | 2024 |
| CP Engineering Services Limited | Aberdeen | 2013 |
| CP22 Ltd | Forfar | 2024 |
| Cpcworldaerotrade INT Limited | London | 2025 |
| CPD Rigging and Lifting Ltd | Wallsend | 2015 |
| CR (NOT Required) Limited | London | 2019 |
| Cradle ARC PLC | London | 2004 |
| Craggan Ltd. | Lossiemouth | 2017 |
| Craigallan Services Limited | Wick | 2018 |
| Craighill Contracts Limited | Hawick | 2020 |
| Craigowl Ltd | Dundee | 2019 |
| Craik Intervention Services Ltd | Dundee | 2022 |
| Crane Ridge Limited | Manchester | 2020 |
| Cranford Geotech Limited | Stafford | 2016 |
| Cranford Stone UK Ltd | Derry | 2021 |
| Cranley Ventures Limited | Aberdeen | 2011 |
| CRB Well Services Ltd | Dundee | 2009 |
| Crcl Brazil Ltd | London | 2024 |
| Creagh Concrete Products Limited | Antrim | 1975 |
| Creasey Crushing-Screening Ltd | Lincoln | 2018 |
| Creative Chemical Solutions Limited | Hoole | 2020 |
| Crebris Ltd | Esher | 2017 |
| Cresla Solutions Limited | London | 2007 |
| Cresswell Petroleum Limited | London | 1993 |
| Crest Technical Services Limited | Purley | 1989 |
| CRG Holdco Limited | Bromley | 2020 |
| CRIDDY4X4 Ltd | Taunton | 2018 |
| Criffel Enterprises Limited | Milton Keynes | 1992 |
| Crimson Aberdeen Limited | Balgownie Road, Bridge Of Don | 2015 |
| Crisco Subsea Ltd | Aberdeen | 2006 |
| Critical Metals PLC | London | 2018 |
| Critical Minerals International Ltd | Ealing | 2024 |
| Crjm Limited | Billingham | 2014 |
| CRM Wise Ltd | Crewe | 2024 |
| Crnco Limited | Aberdeen | 2025 |
| CRO LAX Limited | | 1989 |
| Crockers Contractors Limited | Havant | 2017 |
| Croft Services Ltd | Beverley | 2015 |