| CEL Westoning Clean Energy Reserve Limited | London | 2024 |
| Celaeno Solar Ltd | Bristol | 2020 |
| Celer Installation Services Ltd | Tamworth | 2017 |
| Celestus Energy Limited | London | 2017 |
| Cellarhead Bess Ltd | London | 2020 |
| Cellarhead Green Bess Limited | Cheltenham | 2023 |
| Cello Solar Ltd | Hamilton | 2016 |
| Celsius Air Conditioning Limited | Greater Manchester | 1991 |
| Celsius Aircon Ltd | Exeter | 2019 |
| Celsius Comfort & Control Ltd | Waterlooville | 2022 |
| Celsius Solar Ltd | Troon | 2006 |
| Celtic AID International | London | 2025 |
| Celtic Horizon Offshore Wind Farm Limited | London | 2021 |
| Celtic Sea Offshore Wind Farm Limited | London | 2025 |
| Celtpower Limited | | 1991 |
| Cenfura Consulting Limited | Clapham | 2022 |
| Cenin APV Ltd | Bridgend | 2022 |
| Cenin Gwynt Limited | Bridgend | 2018 |
| Cenin Renewables Limited | Stormydown | 2011 |
| Cenos Offshore Windfarm Ltd | Edinburgh | 2021 |
| Central Area Heat Company Limited | Hungerford | 2016 |
| Central Belt Refrigeration Ltd | Doune | 2017 |
| Central Electrical Services Ltd | Walsall | 1998 |
| Central Hydrogen Ltd | Taunton | 2020 |
| Central Temperature Ltd | Hamilton | 2018 |
| Centre Port Infrastructure Limited | London | 2024 |
| Centre Port Power Limited | London | 2024 |
| Centre Port Terminals Limited | London | 2025 |
| Centrica Barry Limited | Windsor | 2003 |
| Centrica Business Solutions (Generation) Limited | Windsor | 1991 |
| Centrica Distributed Generation Limited | Windsor | 2003 |
| Centrica Energy Assets Holdings Limited | Windsor | 2004 |
| Centrica Energy Marketing Limited | Windsor | 2013 |
| Centrica PLC | Berkshire | 1995 |
| Century Power Limited | Holmfirth | 2024 |
| Cerberus Energy Limited | Torquay | 2006 |
| Ceres (Northampton) Limited | Banbury | 2013 |
| Ceres Energy Limited | Hexham | 2008 |
| Ceres Energy Solutions Limited | Hexham | 2020 |
| Cerulean Winds (Ukcs) Limited | Guildford | 2021 |
| Cerulean Winds Aspen Project Limited | Guildford | 2023 |
| Cerulean Winds Beech Project Limited | Guildford | 2023 |
| Cerulean Winds Cedar Project Limited | Guildford | 2023 |
| Cerulean Winds Limited | Guildford | 2020 |
| CES Green Ltd | Watford | 2023 |
| CES Mechanical Limited | Romford | 2014 |
| Cetis Developments Limited | Stamford | 2004 |
| Ceto Wave Energy UK Limited | Edinburgh | 2013 |
| Cetus Energy (UK) Ltd | Fareham | 2012 |
| Cetus Hydro Energy Ltd | Fareham | 2012 |
| Cetus Marine Ltd | Fareham | 2012 |
| Cetus Technology Ltd | Fareham. | 2004 |
| Cetus Tidal Energy Ltd | Fareham | 2012 |
| Cetus Wave Energy Ltd | Fareham | 2012 |
| Cetus Wind Energy Ltd | Fareham | 2012 |
| Ceunant Hydro CYF | Machynlleth | 2014 |
| Ceylan Aircon UK Ltd | Morden | 2018 |
| Cezar P Pipework Ltd | Stratford-Upon-Avon | 2016 |
| CF Mechanical Ltd | Swanley | 2023 |
| CFP Energy Nominee Limited | London | 2022 |
| CGE Air Conditioning Electrical Ltd | Rochdale | 2026 |
| Cgel Limited | London | 2017 |
| CGN Europe Energy Green Power Holding Limited | London | 2016 |
| CGN Europe Energy UK Holding Limited | London | 2014 |
| CGN Europe Energy Wales Holding Limited | London | 2015 |
| CGP ( South West) Limited | Kingsbridge | 2006 |
| CH Contracts Ltd | Magherafelt | 2018 |
| CH Facilities Services Ltd | Bath | 2023 |
| CH Plumbing & GAS Ltd | Birmingham | 2021 |
| CH Power Ltd | Wrexham | 2025 |
| CHA Power Limited | | 2005 |
| Chadderton Generation Limited | Kirkby Lonsdale | 2016 |
| Chads Farm Energy Centre Limited | Essex | 2020 |
| Chalcroft Solar Power Limited | London | 2013 |
| Chalgrove Green Energy Limited | London | 2025 |
| Chalgrove Solar Limited | Kings Langley | 2013 |
| Chalkdock Biogas Limited | London | 2016 |
| Chalkhill Commercial PV Limited | London | 2015 |
| Challenger Renewables Ltd | London | 2026 |
| Chalton Manor Solar Farm Limited | London | 2019 |
| Chamberlain Knight Electrical Limited | Stockport | 2016 |
| Champ Power Limited | London | 2010 |
| Champion Heating Services Ltd | Coulsdon | 2018 |
| Chandlers Country Properties Limited | Penrith | 2002 |
| Change Energy Supplier Limited | London | 2019 |
| Changingenergy Limited | Ely | 2017 |
| Channel Cable Ltd | Cardiff | 2009 |
| Channel Green Energy Ltd | Bristol | 2021 |
| Channel Solar Limited | London | 2011 |
| Channel Utilities Ltd | Enfield | 2013 |
| Chanson Voltz Limited | Hartlepool | 2025 |
| Chaorach Hydro Limited | Edinburgh | 2013 |
| Chaorainn Hydro Ltd | Leeds | 2017 |
| Chapel Hill Limited | Winchester | 2014 |
| Chapel Lane Energy Storage Holdco Limited | Reading | 2025 |
| Chapel Lane Energy Storage Limited | Reading | 2022 |
| Chapelcross Energy Project Limited | Stockport | 2024 |
| Chapmans Refrigeration Limited | Chatham | 2008 |
| Char.Gy Limited | London | 2016 |
| Charga Ltd | Edinburgh | 2020 |