| Excluss Ltd | Richmond | 2010 |
| Excool Limited | Droitwich | 2010 |
| Excool Pacific Limited | Bromsgrove | 2023 |
| Exegen Limited | Bodmin | 2014 |
| Exelis Energy Ltd | London | 2020 |
| Exergy Solutions Limited | Liverpool | 2021 |
| Exeter Air Conditioning Ltd | Bristol | 2025 |
| Exeter Battery Storage Limited | London | 2025 |
| Exeter RP Limited | Nottingham | 2015 |
| Exeter Storage 2 Limited | London | 2019 |
| Exeter Storage Limited | London | 2022 |
| Exi-Tite Air Filtration Ltd | Dungannon | 2021 |
| Exi-Tite England Ltd | Leatherhead | 2023 |
| Exi-Tite Ltd | Dungannon | 2013 |
| Exi-Tite Scotland Ltd | Glasgow | 2021 |
| Exocore Energy Ltd | London | 2025 |
| Exovolt Smart Energy Limited | London | 2026 |
| Exovolt UK Limited | London | 2026 |
| Expanio Ltd | London | 2026 |
| Expedite Energy Limited | Blackburn | 2016 |
| Expert Bills Saver Limited | Crawley | 2023 |
| Expert Electrical Services (Staffordshire and Cheshire) Limited | Newcastle | 2014 |
| Explorer Heat Limited | Dundee | 2014 |
| Express Energies & Audiovisual Services Ltd | Warrington | 2025 |
| Express Fire Alarms Limited | Hadlow | 2007 |
| Express Mobile Sites Ltd | Liverpool | 2019 |
| Expride Limited | Suffolk | 2025 |
| Extra Energy Supply Limited | Leeds | 2012 |
| Extraction & Ventilation Cleaning Solutions Ltd | Oldbury | 2017 |
| Extrateq Limited | Fareham | 2018 |
| EXWES7 Limited | Shaftesbury | 2010 |
| EYE Renewables Ltd | Glasgow | 2012 |
| EYE Valley Energy Ltd | Glasgow | 2009 |
| EYE Wind Power Limited | London | 2008 |
| Eyeworth Renewable Energy Limited | Sandy | 2011 |
| EYH Enterprises Limited | Biggar | 2013 |
| Eyles Testing Services Limited | Maidstone | 2021 |
| Ezro Utilities Ltd | Mansfield | 2023 |
| F & S Energy Limited | Chelmsford | 2011 |
| F and K (LPG) Engineering Limited | Hampshire | 2003 |
| F B Energy Limited | Guildford | 2015 |
| F&S Ventilation Supplies Ltd | Chelmsford | 2022 |
| FAB16 Limited | London | 2015 |
| Facilities Management (Southern) Ltd | Chandler'S Ford | 2009 |
| Facility Management UK Limited | London | 2000 |
| Factored Energy Services Ltd | Currie | 2025 |
| Fafnir Bess Limited | Bristol | 2021 |
| Fair Deal Utilities UK Limited | Derby | 2023 |
| Fair Energy Savings Ltd | Newcastle Upon Tyne | 2026 |
| Fair Isle Electricity Company Limited | Shetland | 1999 |
| Fair Oaks Renewable Energy Park Ltd | London | 2021 |
| Fair Park Solar Limited | London | 2022 |
| Fairfield Renewables Limited | Enniskillen | 2016 |
| Fairfields Farm Ltd | Lichfield | 2015 |
| Fairgreen Energy Storage Limited | Kings Langley | 2024 |
| Fairlie Biofuels Limited | Forfar | 2015 |
| Fairpower Limited | Heveningham | 2011 |
| Fairview Bess Limited | Stonehouse | 2022 |
| Fairview Farm Limited | Truro | 2011 |
| Fairway Air Ltd | Ashford | 2022 |
| Fairy Hill Community Solar Limited | London | 2022 |
| FAK Blocky Mountain Energy Ltd | Trillick | 2011 |
| Falco Electrical Ltd | Hereford | 2022 |
| Falcontech Enterprises Ltd | Southport | 2022 |
| Falkirk Power Ltd | London | 2021 |
| Falkirk TOD Hill Wind Limited | Warrington | 2010 |
| Fallago RIG Windfarm Limited | Edinburgh | 2001 |
| FAM GAS Group Ltd | London | 2026 |
| Fama Energy Services Limited | Glasgow | 2023 |
| Fanny House Farm Bess Limited | Cheltenham | 2022 |
| Fanny House Solar Farm Limited | London | 2013 |
| Fapd Asia Limited | London | 2023 |
| FAR Leys Wind Limited | Newark | 2013 |
| FAR Marsh Wind Farm Limited | Nottingham | 2014 |
| Faras Electrical Ltd | Hayes | 2018 |
| Farasal Ltd | London | 2022 |
| Faraway Fields Limited | Forfar | 2012 |
| Farleigh Wallop District Heating Limited | Basingstoke | 2014 |
| Farm Energy (N.I) Ltd | Newry | 2013 |
| Farm Energy Services Ltd | Evesham | 2023 |
| Farm Generation Limited | Preston | 2011 |
| Farm Green Energy Limited | Evesham | 2020 |
| Farm Power Apollo Limited | Gatwick | 2011 |
| Farmergy Limited | Blandford | 2006 |
| Farmhill Wind Ltd | Belfast | 2017 |
| Farmoor Energy Limited | Liverpool | 2009 |
| Farnborough Power Limited | Cardiff | 2015 |
| Farndale HV Services Ltd | Guisborough | 2025 |
| Farnese Partners Limited | London | 2016 |
| Farr Windfarm Limited | Edinburgh | 1996 |
| Farrell Farms Limited | Ballymena | 2010 |
| Farringdon Energy Limited | Stansted | 2014 |
| Fartown Wind Ltd | Cookstown | 2012 |
| Fassfern Gridco Limited | Blairgowrie | 2015 |
| Fast Energy Solutions Ltd | Slough | 2022 |
| Fast Places Limited | London | 2024 |
| Fastfix Electrics Limited | Fleet | 2019 |
| Fastned UK Limited | London | 2018 |
| Fastnet Solar 2020 Limited | Weybridge | 2020 |
| Faust Electric Ltd | Peterhead | 2021 |