| Desborough Solar and Battery Storage Limited | Cheltenham | 2023 |
| Desford Renewable Energy Limited | Kettering | 2010 |
| Design and Test Electrical Ltd | Solihull | 2020 |
| Design-Air Limited | Otley | 2013 |
| Designer Electrical Limited | Merrow Lane Guildford | 1995 |
| Deuke Energy Supply Ltd | Greenford | 2025 |
| Devco Upside Latam Ltd | London | 2025 |
| Development Management UK Ltd | London | 2016 |
| Development Ventures Investments Holdings Limited | London | 2024 |
| Devesky Ltd | Belfast | 2014 |
| Devesky Wind Ltd | Carrickmore | 2015 |
| Devine and Associates Drummee Ltd | Enniskillen | 2012 |
| Devine Windfarms Limited | Strabane | 2013 |
| Devizes Solar Limited | London | 2020 |
| Devlin & Sons Contracts Limited | Magherafelt | 2017 |
| Devon Climate Solutions Limited | Newton Abbot | 2025 |
| Devon Electrical & Property Services Limited | Exeter | 2019 |
| Devon Green Power Limited | London | 2022 |
| Devon Power Services Ltd | Devon | 2015 |
| Devon Wind Power Limited | London | 1998 |
| Devpick Limited | Birmingham | 2023 |
| Dewi Roberts CYF | Denbigh | 2014 |
| Dewshill Wind Farm Limited | Huddersfield | 2025 |
| Dexo Ltd | New Malden | 2026 |
| DF Air Conditioning&Heating Ltd | Bournemouth | 2023 |
| DG Charge Limited | London | 2025 |
| DGA ME Holdings Limited | London | 2020 |
| DGJ Consultancy Ltd | Newton Aycliffe | 2021 |
| DGP Energy Ltd | Watford | 2015 |
| Dgpgen Ltd | London | 2023 |
| DGS Plumbing & Heating Ltd | Glasgow | 2019 |
| DH Cold Store Solutions (UK) Limited | Strabane | 2023 |
| DH Wind Solution Ltd | Cowes | 2024 |
| DHG Hydro Limited | London | 1999 |
| DHJ Cooling Ltd | Colchester | 2017 |
| Dhjc Ltd | Derby | 2013 |
| Dhuzz UK Ltd | London | 2025 |
| DIA Home Improvement Ltd | London | 2020 |
| Diadem Bess Limited | Bristol | 2021 |
| Dial-A-Sparky Limited | London | 2016 |
| Diamond Business Solutions Private Limited | Gillingham | 2024 |
| Diamond Cooling Services Ltd | Dartford | 2019 |
| Diamond Cooper Limited | Ulverston | 2025 |
| Diamond Generating Europe Limited | London | 2012 |
| Diamond Green Limited | London | 2017 |
| Diamond Hvac Ltd | Southampton | 2025 |
| Diamond Oryx Limited | London | 2015 |
| Diamond Transmission Corporation Limited | Manchester | 2013 |
| Diamond Transmission Partners BBE (Holdings) Limited | London | 2016 |
| Diamond Transmission Partners BBE Limited | London | 2016 |
| Diamond Transmission Partners DBB (Holdings) Limited | London | 2026 |
| Diamond Transmission Partners DBB Limited | London | 2026 |
| Diamond Transmission Partners Galloper (Holdings) Limited | London | 2017 |
| Diamond Transmission Partners Galloper Limited | London | 2017 |
| Diamond Transmission Partners Hornsea One (Holdings) Limited | London | 2019 |
| Diamond Transmission Partners Hornsea One Limited | London | 2019 |
| Diamond Transmission Partners Hornsea Two (Holdings) Limited | London | 2022 |
| Diamond Transmission Partners Hornsea Two Limited | London | 2022 |
| Diamond Transmission Partners RB (Holdings) Limited | London | 2016 |
| Diamond Transmission Partners RB Limited | London | 2016 |
| Diamond Transmission Partners Sofia (Holdings) Limited | London | 2026 |
| Diamond Transmission Partners Sofia Limited | London | 2026 |
| Diamond Transmission Partners Walney Extension (Holdings) Limited | London | 2017 |
| Diamond Transmission Partners Walney Extension Limited | London | 2017 |
| Diamond Transmission UK Limited | London | 2019 |
| Diamond Wind Limited | Humbie | 2012 |
| Diaspora Solar Connect Limited | Manchester | 2025 |
| Dickie Musdale Windfarm Limited | Oban | 2014 |
| Diddington 1 Limited | Great Yarmouth | 2022 |
| Digima Limited | Radstock | 2008 |
| Digital Energy Revolution Ltd | Wimborne | 2023 |
| Digital Power DM Ltd | London | 2018 |
| Digital Power Energy Supply UK Limited | London | 2017 |
| Digital Power UK Ltd | London | 2022 |
| Digital Screen Solutions Limited | Radstock | 2009 |
| Digitalsurfing Limited | London | 2016 |
| Dimond Electrical Building Services Ltd | Kent | 2004 |
| Diodos Energy Ltd | Aberdeen | 2020 |
| Direct Air Conditioning & Refrigeration Co Ltd | Wallsend | 2014 |
| Direct Air Ltd | London Colney | 2019 |
| Direct Catering Solutions Ltd | Newcastle Upon Tyne | 2020 |
| Direct Cooling & Heating Services Ltd. | Hamilton | 1997 |
| Direct Energy & Utilities Limited | Perth | 2019 |
| Direct Utilities Support Limited | London | 2009 |
| Direct-Energy Associates Limited | Stoke-On-Trent | 2005 |
| Discharger Ltd | London | 2025 |
| Discount Cooling Limited | Loughton | 2026 |
| Discover Solar Ltd | London | 2024 |
| Distgen Brayton LGC Limited | Bristol | 2013 |
| Distgen Faccombe LGC Limited | Bristol | 2011 |
| Distgen Hinton LGC PLC | Bristol | 2013 |
| Distgen Rogershill LGC PLC | Bristol | 2012 |
| Distgen Wanstrow LGC Ltd | Bristol | 2013 |
| Distilled Bioenergy Limited | Guildford | 2024 |
| Distington Moss Wind Farm Limited | Harrogate | 2025 |
| Distributed Energy Customer Solutions Limited | Windsor | 2003 |
| Distributed Energy Solutions Limited | Henley-On-Thames | 2024 |
| Distributed Generation Ltd | Bristol | 2018 |
| Distributed Solar Energy Limited | Norwich | 2011 |
| Distribution Jointing Services Ltd | Huddersfield | 2022 |