| Distribution Project Services Ltd | Chester Le Street | 2022 |
| District Energy Aberdeen Limited | Edinburgh | 2013 |
| Ditcheat Solar CIC | Redruth | 2024 |
| Ditcher Law Limited | Edinburgh | 2022 |
| Diverse Cooling Solutions Ltd | Blackburn | 2011 |
| Dixon Engineering (Air Conditioning) Limited | Didcot | 1994 |
| DJC Consultancy Limited | Southport | 2020 |
| DJM Electrical Installations Limited | Epping | 2016 |
| DJO Hvac Services Ltd | Bromsgrove | 2025 |
| DJS Air Conditioning Ltd | Gravesend | 2020 |
| DJS Electrical Contractors Ltd | Sheerness | 2017 |
| DJS Offshore Ltd | Hexham | 2021 |
| DKA2 Ltd | Poole | 2026 |
| DKE Air Conditioning & Refrigeration Ltd | Peterborough | 2022 |
| DKF & F Ltd | Beckenham | 2023 |
| Dking Electrical Ltd | Milton Keynes | 2018 |
| DL Green Energy Ltd | Huddersfield | 2012 |
| Dlec Renewables Ltd | Fareham | 2023 |
| DLM Air Solutions Limited | Brigg | 2011 |
| DLR Cooling Services Limited | Birmingham | 2016 |
| DM Electrical Installations (NW) Ltd | Macclesfield | 2025 |
| DM Jointing Ltd | Sheffield | 2024 |
| DM Solar Limited | Cardiff | 2013 |
| DMD Electrics Ltd | St. Albans | 2007 |
| DMH Air Conditioning Ltd | Bradford | 2022 |
| DMH Electrical Services Ltd | York | 2023 |
| DMK Mechanical Services Limited | Stoke On Trent | 1996 |
| DMM GAS Services Limited | London | 2025 |
| DMP Renewable Consultancy Limited | Sunderland | 2018 |
| Dmtn Limited | Dumfries | 2016 |
| Dmundie Electrical Limited | Bo'Ness | 2025 |
| DN Cable Installations Limited | Sidcup | 2019 |
| DN Mechanical Services Ltd | Liverpool | 2022 |
| DN Rigging & Lifting Ltd | Aberdeen | 2024 |
| DNA Global Energy Ltd | London | 2019 |
| DNA Global Partners Ltd | London | 2019 |
| Dnkat Ltd | Northolt | 2016 |
| DNR Electrical Ltd | Westgate-On-Sea | 2017 |
| Dochfour Enterprises Limited | Inverness | 2014 |
| Docking Farm Solar Limited | London | 2020 |
| Dodoma Ventures Limited | Belfast | 2017 |
| Doggerbank Offshore Wind Farm Project 1 Holdco Limited | Reading | 2017 |
| Doggerbank Offshore Wind Farm Project 2 Holdco Limited | Reading | 2017 |
| Doggerbank Offshore Wind Farm Project 3 Holdco Limited | Reading | 2017 |
| Dolcynafon Hydro CYF | Dolgellau | 2018 |
| Dolgellau Energy Cwmni Buddiant Cymunedol | Dolgellau | 2023 |
| Dolhendre Hydro Limited | Mold | 2012 |
| Dollymans Storage Limited | London | 2017 |
| Dolphyn Hydrogen - Celtic Sea SPV Limited | London | 2022 |
| Dolphyn Hydrogen - North Sea SPV Limited | London | 2022 |
| Dolphyn Hydrogen Limited | London | 2022 |
| Dolywind Ltd | Newtown | 2025 |
| Domestic Aircon Solutions Ltd | West Drayton | 2022 |
| Domino Energy Limited | London | 2016 |
| DON Cossack Ltd | London | 2020 |
| DON Giuliano Ltd | Swindon | 2024 |
| Donald ( SAP ) Services Limited | Wallsend Upon Tyne | 2013 |
| Donanside Limited | Girvan | 2023 |
| Donard Wind Limited | Belfast | 2016 |
| Doncaster Lighting Limited | South Yorkshire | 2004 |
| Doncaster Power (10MW) Limited | Driffield | 2018 |
| Doncaster Power 16MW Limited | Driffield | 2023 |
| Doncaster Power Projects Limited | Driffield | 2022 |
| Doncutt 2023 Limited | Tamworth | 2023 |
| Donoma Power Limited | Bristol | 2010 |
| Doodson Electrical Limited | Halifax | 2017 |
| Doogary Renewables Ltd | Omagh | 2013 |
| Dooish Wind Farm Limited | Belfast | 2007 |
| Doon Wind Limited | Enniskillen | 2013 |
| Dopower Limited | Matlock Bath | 1991 |
| Dorenell Windfarm Extension Limited | Cardiff | 2020 |
| Dorians Plumbing & Heating Ltd | Barnet | 2019 |
| Dorothea Pumped Hydro Limited | St Asaph | 2017 |
| Dorset PAT Testing Ltd | Weymouth | 2020 |
| Dorset Solar Limited | Stalbridge | 2020 |
| Dougall Power Installations Ltd | Glasgow | 2016 |
| Douglas Community Ecoheat Limited | Douglas | 2010 |
| Douglas West Extension Ltd | Aberdeen | 2018 |
| Douglas West Wind Farm Ltd | Edinburgh | 2016 |
| Douglas Winters Associates Limited | Chelmsford | 2011 |
| Dove Renewables Ltd | Totnes | 2016 |
| Dove View Solar Farm Limited | Hove | 2014 |
| Dovecote Systems Ltd | Southampton | 2026 |
| Doves Moor Energy Park Limited | Exeter | 2025 |
| Dowlais Top Wind Limited | Cheltenham | 2023 |
| Dowls M&E Ltd | Ormskirk | 2022 |
| Down at Hele Limited | Okehampton | 2010 |
| Down Barn Farm SF Limited | London | 2014 |
| Downiebrae Bess Ltd | Ross-On-Wye | 2023 |
| Downiebrae EV Ltd | Ross-On-Wye | 2024 |
| Downing Energy Development Company Limited | London | 2020 |
| Downing Renewable Developments Grid Co Limited | London | 2024 |
| Downing Spares Limited | London | 2022 |
| Doyletech (Essex) Ltd | Basildon | 2018 |
| DPB Electrical Limited | Littleborough | 2016 |
| DPR Electrical Ltd | Blackpool | 2019 |
| DPS Ecotech Limited | Nottingham | 2011 |
| DPS Electrical Contractors Limited | Ipswich | 2014 |
| DR Air CON Ltd | Rochester | 2023 |
| DR Electrics Ltd | Stanion | 2015 |