| Business Utility Advisors Ltd | Penn Street | 2011 |
| Business Utility Limited | London | 2023 |
| Bute Energy (Cambria) Limited | Cardiff | 2020 |
| Bute Energy Construction Holdings Limited | Cardiff | 2025 |
| Bute Energy Limited | Cardiff | 2020 |
| Bute Energy NB Limited | Cardiff | 2026 |
| Butlers Wood Bess Limited | Cheltenham | 2022 |
| Butlers Wood NG Limited | London | 2022 |
| Butteriss Downs Solar Farm Limited | Gatwick | 2011 |
| Buttsbury Electrical Ltd | Brentwood | 2019 |
| Buxton + Mcnulty Mechanical Services Limited | Erith | 2005 |
| Buy Air Conditioning Ltd | London | 2020 |
| Buyinfo Limited | Norfolk | 1994 |
| Buzcart Limited | West Kilbride | 2014 |
| BV Renewables Ltd. | Glasgow | 2010 |
| Bvalony UK Limited | Orpington | 2022 |
| BVG Electrical Services Limited | Slough | 2016 |
| BW ESS Asset UK Limited | London | 2025 |
| BW ESS AUS Holdco Limited | London | 2026 |
| BW ESS UK Limited | London | 2022 |
| BW Holdco Ltd | Aberdeen | 2018 |
| BW Plumbing & Heating Ltd | Ossett | 2015 |
| Bwave Ltd | London | 2025 |
| BWE (5) Ltd | Edinburgh | 2013 |
| BWE (6) Ltd | Peterhead | 2015 |
| BWE (7) Ltd | Edinburgh | 2014 |
| Bwlch Gwyn Wind Farm Limited | Mold | 2021 |
| Bwrx Limited | Bristol | 2024 |
| Bwsc Generation Services Northern Ireland Ltd | Londonderry | 2015 |
| Bwsc Generation Services UK Ltd | Sleaford | 2013 |
| By-Pass Farm Solar Limited | Reading | 2020 |
| Byerley Energy Limited | Warrington | 2014 |
| Bygd HF Limited | St. Asaph | 2024 |
| Bygen (Chippenham) Ltd | King'S Lynn | 2023 |
| Bygen Power (Tregeen) Limited | King'S Lynn | 2016 |
| Bygen Power Limited | King'S Lynn | 2007 |
| Bypass Nurseries Lspv Limited | London | 2013 |
| Byres Generation Ltd | Longniddry | 2011 |
| Byrne Green Energy Ltd | Omagh | 2016 |
| Bytewise System Services Limited | Biggleswade | 1990 |
| C & C (SW) Limited | Plymouth | 2014 |
| C & G Renewables Limited | London | 2011 |
| C & K Management Consultancy Ltd | Bracknell | 2017 |
| C & M Hall Limited | Huddersfield | 2005 |
| C & N Pipeline Limited | Birmingham | 2017 |
| C & R Utilities Ltd | Billingham | 2010 |
| C & S Energy Limited | Reading | 2021 |
| C Aldridge Utilities Limited | Southminster | 2018 |
| C E Avonmouth Turbine Ltd | Wadebridge | 2012 |
| C G LEE Electrical Engineers Limited | Leeds | 2006 |
| C Haste Limited | Stockton-On-Tees | 2025 |
| C Humm Utilities Limited | Orpington | 2019 |
| C J DIX Plumbing Ltd | Folkestone | 2012 |
| C J Matthews Ltd | Tonbridge | 2024 |
| C L J Connect Limited | Leeds | 2007 |
| C LEC Limited | Pevensey Bay | 2023 |
| C M R Electrical Limited | Uckfield | 2003 |
| C M W Utilities Limited | Bishop Auckland | 2008 |
| C S Renewables Limited | Armagh | 2018 |
| C Stefanescu Electrical Services Limited | Woodford Green | 2014 |
| C W Electrical Installation Ltd | Church Lawton | 2008 |
| C&N Electrical Services Ltd | Portland | 2017 |
| C&P GAS Services Limited | Durham | 2018 |
| C-L Munn Utilities Limited | Stoke-On-Trent | 2024 |
| C. Allen Electrical Ltd | Bournemouth | 2015 |
| C.A. Strawson Energy Limited | Newark | 1976 |
| C.B. Air Conditioning Limited | Newcastle | 2003 |
| C.D Electrical Design & Installation Limited | Nuneaton | 2008 |
| C.H.E.S Ltd | Swansea | 2014 |
| C.Halliwell GAS Services Limited | Wigan | 2020 |
| C.P.R Security Ltd | Birmingham | 2022 |
| C.S.Projects UK Limited | Manchester | 2009 |
| C.V. A.C Limited | London | 2018 |
| C4 GAS Limited | London | 2009 |
| CAB GAS Ltd | Newcastle Upon Tyne | 2023 |
| Cabilla Energy Ltd | Bodmin | 2010 |
| Cable Repair Services Limited | Northfleet | 2017 |
| Cabragh Energy Ltd | Belfast | 2025 |
| CAD Air Conditioning Limited | Farnborough | 2004 |
| Caddick Renewables Limited | Wetherby | 2012 |
| Cadent GAS Limited | Coventry | 2016 |
| Cadogan Energy Holdings Limited | London | 2021 |
| Cadoxton Reserve Power Limited | Bristol | 2014 |
| Cadzow Energy Storage Limited | Stokesley | 2021 |
| CAE1 Solar Limited | Bristol | 2026 |
| Caeli Refrigeration Ltd | Birmingham | 2020 |
| Caepen Limited | Pwllheli | 2015 |
| Caergarw Green Energy Park Limited | London | 2023 |
| Cafferkey Electrical Contractors Limited | Nottingham | 2014 |
| Caicias Energy Limited | London | 2016 |
| Cailleach Offshore Windfarm Limited | London | 2021 |
| Cairds Hill Wind Farm Limited | Edinburgh | 2025 |
| Cairn Duhie Energy Limited | Kings Langley | 2022 |
| Cairnadailly Wind Turbine Limited | Ellon | 2015 |
| Cairnborrow Wind Energy Limited | London | 2008 |
| Cairnhill Energy C.I.C. | Banff | 2015 |
| Cairnhill Renewable Energy Ltd | Glasgow | 2015 |
| Cairnhill Solarfield Limited | London | 2014 |
| Cairnhill Wind and Solar Limited | London | 2014 |
| Cairnhill Windfarm Limited | Glasgow | 2008 |