| IBE Old Works Limited | Chester Le Street | 2025 |
| IBE Polegate Limited | County Durham | 2023 |
| IBE Salts Road Limited | Chester Le Street | 2022 |
| Ibekk Ltd | Bolton Lancs | 2021 |
| Ibexia Global Development Ltd | London | 2019 |
| IBG 1 Ltd | Romford | 2019 |
| Ibip Holding Limited | Belfast | 2017 |
| IBV Barlings Solar Ltd | London | 2024 |
| IBV Birtles Hill Energy Park Ltd | London | 2025 |
| IBV Brinkburn Energy Park Limited | London | 2025 |
| IBV Burdiehouse Energy Park Limited | London | 2025 |
| IBV Burnfoot Energy Park Limited | London | 2025 |
| IBV Clay Hills Energy Park Ltd | London | 2025 |
| IBV Coachford Energy Park Ltd | London | 2025 |
| IBV Danethorpe Lane Solar Limited | London | 2025 |
| IBV Elford Park Solar Limited | London | 2025 |
| IBV Fordgate Solar Limited | London | 2025 |
| IBV Kelfield Solar Ltd | London | 2025 |
| IBV Knorren Beck Solar Ltd | London | 2025 |
| IBV Luscott Barton Solar Ltd | London | 2025 |
| IBV Mire Beck Energy Park Ltd | London | 2025 |
| IBV Norrington Energy Park Ltd | London | 2025 |
| IBV Oakland Energy Park Ltd | London | 2025 |
| IBV Thorpe-In-The-Fallows Solar Farm Ltd | London | 2026 |
| IBV Thrift Solar Limited | London | 2025 |
| IBV Tickhill Solar Limited | London | 2024 |
| IBV Torness Energy Park Limited | London | 2025 |
| IBV Weald Place Farm Limited | London | 2025 |
| IBV West Ghyll Energy Park Ltd | London | 2025 |
| IBV West House Energy Park Ltd | London | 2025 |
| IBV West Melton Solar Park Limited | London | 2025 |
| IBV Willington Energy Park Limited | London | 2025 |
| Icarus Energy Ltd | Exeter | 2022 |
| Icarus Solar Ltd | West Malling | 2022 |
| Icarus Solar Park Limited | Newark | 2026 |
| ICD Energy Training Academy Ltd | Rotherham | 2017 |
| Iceboys Limited | Milton Keynes | 1999 |
| Icelend Ltd | Orpington | 2025 |
| ICG Site Facilities Management Ltd | High Wycombe | 2025 |
| Icknield GAS Limited | Reading | 2014 |
| Icona 6 Ltd | Manchester | 2021 |
| Iconnect Electrical Services UK Limited | Oldham | 2017 |
| Icool Air Conditioning Limited | Basildon | 2023 |
| Icool Environmental Ltd | Bromley | 2020 |
| Icyco Ltd | Kingston Upon Thames | 2021 |
| ID Bladeworks Ltd | Invergordon | 2024 |
| Idbutt Consulting Ltd | Atherstone | 2005 |
| Iddenshall Solar Limited | London | 2022 |
| Ideal Air Solutions Ltd | London | 2023 |
| Ideal Aire Ltd | Gloucester | 2025 |
| Idee Solis Ltd | London | 2026 |
| IE Billingham Works Ltd | Tamworth | 2025 |
| IE Eggborough Station Ltd | Tamworth | 2025 |
| IEG Utilities Limited | Southend-On-Sea | 2024 |
| Ienergi Group Limited | London | 2023 |
| Ifixcommercial Limited | Dundee | 2018 |
| IFM Master Holdco Limited | London | 2019 |
| Ifusion Volt Ltd | London | 2026 |
| Iglobe Platinum FD III Limited | Durham | 2025 |
| Igloo Aircon Limited | London | 2024 |
| Igloo Energy Supply Limited | Brighton | 2015 |
| Ignite Blue Flame Ltd | London | 2024 |
| Ignite Energy Consultants Ltd | Manchester | 2024 |
| IGO Ventures Ltd | Poole | 2023 |
| Igocorp Limited | Bournemouth | 2020 |
| Igrids Ltd | London | 2026 |
| IIR Services (UK) Limited | Leicester | 2014 |
| IJM Wind Ltd | Newcastle Upon Tyne | 2021 |
| Ikegrid Ltd | Nottingham | 2026 |
| Ikonic Renewables Limited | Heywood | 2024 |
| IL Solar Limited | London | 2020 |
| IL-UKI-020 Mill Farm Ltd | London | 2026 |
| IL-UKI-023 Western Sutton Ltd | London | 2026 |
| IL-UKI-031 Old House Ltd | London | 2026 |
| Iladia Limited | Wimborne | 2019 |
| Ilford Electricians Ltd | Dagenham | 2020 |
| ILI (Craigthornhill) Limited | Glasgow | 2014 |
| ILI (MID Brockloch) Limited | Elgin | 2013 |
| ILI (Skellyton) Limited | Glasgow | 2012 |
| ILI (Tanhill Farm) Limited | Motherwell | 2011 |
| ILI (Yonderton) Limited | Forss By Thurso | 2011 |
| Ilkeston Power Limited | Nottingham | 2015 |
| Ilos Firsby Lane Ltd | London | 2022 |
| Ilos Hoopers Pool Ltd | London | 2022 |
| Ilos Hunston Ltd | London | 2022 |
| Ilos Little Flanchford Ltd | London | 2022 |
| Ilton Solar Limited | Bradford-On-Avon | 2023 |
| IM2 Fred BES Limited | London | 2024 |
| IM2 Power Asset Co Limited | London | 2023 |
| IM2 Power UK Limited | London | 2023 |
| IM2 Solar Project 1 Ltd | London | 2022 |
| Imai Solar Ltd | Bristol | 2022 |
| Imgreen Ltd | Crawley | 2025 |
| Immingham Energy Limited | London | 1999 |
| Immingham Energy Storage Limited | London | 2024 |
| Immingham Power Limited | Bristol | 2017 |
| Immortal Energy International Ltd | Newcastle Upon Tyne | 2021 |
| Impact PM Limited | London | 2014 |
| Imparator Green Energy Ltd | Dartford | 2011 |
| Impello Limited | London | 2002 |