| Ductwork Erection Services Ltd | Glasgow | 2009 |
| Dudgeon Offshore Wind Limited | London | 2002 |
| DUE South Group Limited | Windsor | 2019 |
| Dullerton Road Ltd. | Belfast | 2012 |
| Dulsie Wood Wind Farm Limited | Edinburgh | 2023 |
| Dummuies Windfarm Huntly Limited | London | 2005 |
| DUN Law 1 Repowering Limited | Bristol | 2026 |
| Dunaird Energy Ltd | Broughshane | 2026 |
| Dunan Power Company Limited | London | 2014 |
| Dunbar Bess Limited | London | 2025 |
| Dunbarton Bess Ltd | Wadebridge | 2024 |
| Dunbear EV Limited | Motherwell | 2026 |
| Dunbeg South Energy Limited | Larne | 2021 |
| Dunbeg Windfarm Limited | Belfast | 2010 |
| Dunbunraver Power Ltd | Newtownstewart | 2020 |
| Dundee Merchant Wind Park Limited | Stroud | 2002 |
| Dundee University Utility Supply Company Limited | | 1990 |
| Dunedin Electrical Ltd | Edinburgh | 2024 |
| Dunkeswell G1 Solar Farm Limited | Hove | 2014 |
| Dunlogan Hydro Ltd | Magherafelt | 2014 |
| Dunmaglass Wind Farm Limited | Perth | 2018 |
| Dunmill Energy Storage Limited | Kings Langley | 2022 |
| Dunmore 2 Wind Farm Ltd | Belfast | 2012 |
| Dunmore Renewable Energy Ltd | Bedford | 2010 |
| Dunmore Wind Farm Ltd | Belfast | 2011 |
| Dunmow Solar Limited | Bristol | 2022 |
| Dunnaree Hill Wind Farm Ltd | Lisburn | 2026 |
| Dunndee GAS Limited | Dundee | 2024 |
| Dunning Futures Limited | Widnes | 2022 |
| Dunnockshaw Developments Limited | Great Sankey | 2026 |
| Dunphail II Windfarm Limited | Edinburgh | 2018 |
| Dunphail Windfarm Limited | Edinburgh | 2018 |
| Dunscroft Wind Farm Limited | London | 2025 |
| Dunston (Ship Repairers) Limited | Driffield | 1993 |
| Dunwan DAM Wind Farm Limited | Huddersfield | 2026 |
| Dupplin Renewable Energy Company Limited | Perth | 2018 |
| Duranta Energy Services Limited | Middlesbrough | 2012 |
| Duranta Teesside Limited | Middlesbrough | 2012 |
| Durare Ltd | Nottingham | 2025 |
| Durham RP Limited | Nottingham | 2018 |
| Durham Solar 1 Limited | Northampton | 2020 |
| Duro Climate Design Ltd | Sutton Coldfield | 2016 |
| Duror Hydro Ltd | St Albans | 2017 |
| Durpley WT Limited | London | 2013 |
| Durris Wind Farm Limited | Maidenhead | 2021 |
| Durweston Hydro Limited | Maidenhead | 2015 |
| Durweston Mill Water Limited | Dorset | 2005 |
| Duty to Energy Limited | Kettering | 2022 |
| DV Global Imports Ltd | London | 2025 |
| DV8 CPO Limited | London | 2025 |
| DW Energy Ltd | Durham | 2026 |
| DW GAS Solutions Ltd | Leeds | 2021 |
| DW Midlands Electrical Limited | Swadlincote | 2018 |
| DWD MON Electrical Limited | Ellesmere Port | 2025 |
| DWE Power Ltd | Cleveleys | 2016 |
| DWI (NI) Limited | Londonderry | 2013 |
| DWR Maesglas CYF | Machynlleth | 2012 |
| DWR NWY Trydan Holdings Limited | Bristol | 2015 |
| DWR Pontfaen Limited | London | 2010 |
| DWS Elec Ltd | Blackpool | 2017 |
| DY Energy Solutions Limited | Ilford | 2024 |
| DY Oldhall Energy Recovery Limited | London | 2019 |
| Dyce Energy Electricity Ltd | Rotherham | 2024 |
| Dyce Energy GAS Ltd | Rotherham | 2024 |
| Dyce Energy Limited | Rotherham | 2016 |
| Dyce Utilities Limited | Rotherham | 2019 |
| Dyfed GAS Limited | Pembroke Dock | 2022 |
| Dyffryn Brodyn Limited | London | 1994 |
| Dyffryn Crawnon Green Energy Community Interest Company | Crickhowell | 2009 |
| Dyfodol Borth Future Ltd | Borth | 2024 |
| Dykelands Windfarm Limited | Edinburgh | 2014 |
| Dynamic Energy Solutions Holdings Ltd | Petersfield | 2019 |
| Dynamic Epower Holdings Limited | Ashford | 2017 |
| Dynamic Maintenance Group Limited | Cardiff | 2020 |
| Dynamiq Energy Solution Ltd | London | 2025 |
| Dynamis Energy Limited | Glasgow | 2024 |
| Dynamix Energy Limited | Aberdeen | 2021 |
| Dynamo EV Ltd | St Helens | 2025 |
| Dynatech Renewables Ltd | Wallsend | 2022 |
| Dynorotor Limited | London | 2020 |
| Dysart Energy Limited | Magherafelt | 2012 |
| Dyse EV Ltd | Stourbridge | 2023 |
| E & D Air Conditioning Ltd | London | 2019 |
| E & I Trading Services Limited | Ashby-De-La-Zouch | 2010 |
| E (GAS and Electricity) Limited | Wetherby | 2013 |
| E a C Technical Services Limited | Swansea | 2026 |
| E C Eco Energy Limited | Sawbridgeworth | 2023 |
| E D F Trading Limited | London | 1999 |
| E E Solutions Limited | Leeds | 2008 |
| E G Solar Limited | Brough | 2015 |
| E Grid Services Limited | Belfast | 2023 |
| E R Electrical Ltd | Wandsworth | 2016 |
| E Vehicle Charging Limited | Melton Mowbray | 2021 |
| E&G Energy Solution Limited | London | 2013 |
| E&G Plumbing Heating Ltd | London | 2019 |
| E&L Electrical Services Limited | Johnstone | 2025 |
| E-Clipse Plumbing and Heating Ltd | Addlestone | 2014 |
| E-Drive Energy Limited | London | 2026 |
| E-Electrical Solutions Ltd | Rainham | 2023 |
| E-Gas Service Ltd | Paisley | 2025 |