| Calva View Limited | Sunderland | 2024 |
| Calvert Petrophysics Limited | Surbiton | 2023 |
| Calyx Global Solutions Ltd | London | 2025 |
| CAM Chalk Ltd | Cambridge | 2020 |
| Cambrian Carbon Limited | Cardiff | 2025 |
| Cambrian Environmental Technologies Limited | Cardiff | 2001 |
| Cambrian Services Limited | Ruthin | 2018 |
| Cambrian Stone Limited | Birmingham | 1981 |
| Cambrian Water Limited | Cardiff | 2025 |
| Cambridge Carbonates Limited | Solihull | 1993 |
| Cambridge Design Partners Ltd | London | 2021 |
| Cambridge Global Solutions Ltd | London | 2025 |
| Camlough Aggregates Ltd | Dungiven | 2022 |
| Cammach Group Limited | Keith | 1997 |
| Cammach More Unlimited | Keith | 2011 |
| Camoco Limited | Aberdeen | 2003 |
| Campbell Contracts Ltd | Co Fermanagh | 2002 |
| Campbell Geoservices Limited | Dunfermline | 2015 |
| Campbell Quarries Ltd | Enniskillen | 2025 |
| CAN (Global) Limited | London | 2004 |
| CAN (Offshore) Limited | London | 1986 |
| Canada Bioco Co., Ltd | Beckenham | 2024 |
| Canada Domile Chemical Group Co., Ltd | Cardiff | 2026 |
| Canada Esif International Group Limited | Cambridge | 2026 |
| Canada Green Nutrien Chemicals Ltd | Cambridge | 2024 |
| Canada MAX Crop Nutrition Co., Ltd | Cambridge | 2024 |
| Canada Nicee Greenhouse Gardening Co., Ltd | Cambridge | 2026 |
| Canada Valadiro Plant Nutrition Company Co., Ltd | Cardiff | 2026 |
| Canadian Kaisenrui International Fertilizer Co., Ltd | Cambridge | 2025 |
| Canadian Overseas Petroleum (UK) Limited | Sutton | 2009 |
| Canesis Data Ltd | Hawarden | 2003 |
| Canuk Petroleum Engineering Services Limited | Carnoustie | 2011 |
| CAP Energy PLC | London | 2005 |
| Capacity Minerals Ltd | Saltburn-By-The-Sea | 2025 |
| Cape Site Services Limited | Barnsley | 1995 |
| Capital Aggregates Limited | London | 2017 |
| Capital City Access Ltd | Dalkeith | 2023 |
| Capps-Jenner Services Limited | Lowestoft | 2016 |
| Capricorn Americas Limited | Edinburgh | 2017 |
| Capricorn Coal Limited | Guildford | 2019 |
| Capricorn Egypt (Holding) Limited | London | 2020 |
| Capricorn Egypt Limited | London | 2020 |
| Capricorn Energy Holdings Limited | Edinburgh | 2008 |
| Capricorn Energy Investments Limited | Edinburgh | 2021 |
| Capricorn Energy PLC | Edinburgh | 2002 |
| Capricorn Energy UK Limited | London | 2002 |
| Capricorn LOW Carbon Solutions Limited | London | 2021 |
| Capricorn Mauritania Limited | Edinburgh | 2013 |
| Capricorn OIL Limited | Edinburgh | 2006 |
| Capricorn Petroleum Limited | Edinburgh | 2007 |
| Capricorn Resources Management Limited | Edinburgh | 2001 |
| Capricorn Resources PLC | | 2002 |
| Capricorn Senegal Limited | Edinburgh | 2013 |
| Capsole Limited | Edinburgh | 2017 |
| Caradon Ltd | Liskeard | 2020 |
| Carbon Storage Partners Ltd | Godstone | 2024 |
| Carbonarc Global Ltd | Bodmin | 2026 |
| Carbonchain.Io Limited | London | 2017 |
| Carci Mining Consultants Ltd | Caterham | 2019 |
| Cardigan Sand and Gravel Company Limited | Cardigan | 1959 |
| Cardross Offshore Services Ltd. | Dumbarton | 2011 |
| Carey Offshore Services Ltd | Beccles | 2009 |
| Caribbean Goldfields Limited | London | 2020 |
| Caribx (UK) Limited | Marlow | 2009 |
| Carina Royalties Limited | London | 2022 |
| Carleg Limited | Whitby | 2013 |
| Carmel's Limited | Aylesbury | 2002 |
| Carn Minerals Limited | Cornwall | 2026 |
| Carnie Drilling and Engineering Ltd | Montrose | 2018 |
| Carramac Limited | Slough | 2022 |
| Carreg TEC Limited | Chepstow | 2015 |
| Carreg Trefor CYF | Caernarfon | 2025 |
| Carrick Resources Limited | Southampton | 2016 |
| Carrickcrua Limited | Newry | 2025 |
| Carse Services Ltd | Montrose | 2008 |
| Carson Resources Limited | Aberdeen | 2003 |
| Cashty Quarry Ltd | Omagh | 2022 |
| Casimir Consulting Limited | London | 2004 |
| Casinro Ltd | Glasgow | 2019 |
| Caspian Consultants Limited | London | 2002 |
| Caspian OIL & Energy Limited | London | 2002 |
| Caspian Quality Services Ltd | London | 2025 |
| Caspian Sunrise PLC | London | 2006 |
| Cassidy Advisory Limited | Glasgow | 2023 |
| Cassl Construction Limited | Buckie | 2018 |
| Cast Consulting Ltd | Lytham St. Annes | 2015 |
| Castle Acre Quarry Limited | Swaffam | 2020 |
| Castle Hill Quarry Co.,Limited | Bridgwater | 1941 |
| Castle Stone Limited | Neath | 2015 |
| Castle View Geology Limited | Alness | 2019 |
| Castlecomer Properties Limited | Sevenoaks | 1998 |
| Catalina Resources PLC | Malvern | 2006 |
| Cath DDU Energy Ltd | Caldicot | 2014 |
| Cathay Energy Ltd | Cardiff | 2016 |
| Catoxy Energy Ltd | London | 2025 |
| Cats North Sea Limited | London | 2014 |
| Catwick Farm Minerals Ltd | Whitby | 2012 |
| Cavan Fermanagh Leitrim Community Group CIC | Enniskillen | 2021 |
| Cavelstone Aggregates Limited | Lochgelly | 2023 |
| Cavern International Limited | London | 2024 |