| Hutton Hall Turbines Limited | Richmond | 2015 |
| Hutton Solar Limited | London | 2024 |
| Hutz Medical UK Limited | London | 2021 |
| HV & LV Power Solutions Ltd | Bude | 2024 |
| HV Electrical Ltd | Annan | 2018 |
| HV Energy Ltd | Grimsby | 2024 |
| HV Management Ltd | Ludlow | 2024 |
| HV Operational Solutions Ltd | Sutton Valence | 2024 |
| HV Power Limited | Birmingham | 2011 |
| Hvac Energy Solutions Limited | Glasgow | 2008 |
| Hvac Studio Ltd | London | 2019 |
| Hvac Units Limited | Whitchurch | 2025 |
| Hvaciq Limited | Worcester | 2023 |
| Hvacuk Ltd | Manchester | 2019 |
| HVC Group Limited | Ballyclare | 2026 |
| Hviid Energy Ltd | Wadhurst | 2009 |
| Hvmh Engineering Limited | Brighton | 2021 |
| HVS Gridco Ltd | London | 2020 |
| HVS Siteco Ltd | London | 2020 |
| HW Solar Farm Limited | Bristol | 2021 |
| HY Fiachra Energy Ltd | Plymouth | 2013 |
| Hy-Gen Power Limited | London | 2020 |
| Hy-Save (UK) Limited | Radstock | 1998 |
| Hybont Limited | Oxford | 2023 |
| Hybrid Car Charge Limited | Petersfield | 2017 |
| Hybrid Cooling Ltd | London | 2023 |
| Hybrid Energy Solutions Ltd | London | 2021 |
| Hybrid Future Ltd | Manchester | 2018 |
| Hybrid Solar Solutions Ltd | Middlesbrough | 2023 |
| Hyde Farm Solar Limited | Reading | 2015 |
| Hydragon Motor Company Ltd | Pencoed, Bridgend | 2006 |
| Hydrixon Tech Ltd | Wotton-Under-Edge | 2025 |
| Hydro Auto-Energies Ltd | London | 2023 |
| Hydro Dynamic BBC Ltd | Stanmore | 2026 |
| Hydro Energy Trading Limited | Norwich | 2014 |
| Hydro Genpower Limited | Londonderry | 2020 |
| Hydro Kinetic Power Ltd | Borehamwood | 2021 |
| Hydro Ludens Holdings Limited | Glasgow | 2020 |
| Hydro Ludens Limited | Glasgow | 2016 |
| Hydro Mill Group Limited | Exeter | 2016 |
| Hydro Power Ireland Limited | Belfast | 2014 |
| Hydro Schemes UK Ltd | Aberaeron | 2010 |
| Hydro Ventures Ltd. | Colchester | 2024 |
| Hydro-Energy Limited | Corby | 2011 |
| Hydro-Ready Limited | Abbots Langley | 2025 |
| Hydrogen Mobile Generators Scotland Limited | Glasgow | 2023 |
| Hydrogen Networks Limited | Wokingham | 2020 |
| Hydrogen Trading Ireland Limited | Dundonald | 2020 |
| Hydrogenie Services Ltd | Hampstead | 2018 |
| Hydromatch Ltd | Cullompton | 2005 |
| Hydron Pumps Limited | Sheffield | 2018 |
| Hydropower River Leven Ltd | Perth | 2018 |
| Hydropulse Limited | Sheffield | 2025 |
| Hydrosense Renewables Limited | Totnes | 2012 |
| Hydroshoal Limited | Buckie | 2012 |
| Hydrostor UK Ltd | Milton Keynes | 2024 |
| Hydrowing Tidal Projects Limited | Gaerwen | 2022 |
| Hydrus Renewables Limited | Quorn | 2013 |
| Hyhaul Mobility Limited | Cardiff | 2021 |
| Hyready Ltd. | Glasgow | 2020 |
| Hyve'Ed CIC | Telford | 2025 |
| Hyway Cabling Ltd | Slough | 2014 |
| Hywind (Scotland) Limited | London | 2013 |
| I AM Electric Limited | London | 2013 |
| I AM Energy Ltd | Nottingham | 2020 |
| I Delta Heating and Electrical Specialist Limited | Bexhill-On-Sea | 2019 |
| I E Energy Limited | Stoke-On-Trent | 2019 |
| I E Energy Storage Limited | Stoke-On-Trent | 2019 |
| I E Group Limited | Stoke-On-Trent | 2019 |
| I E Renewables Limited | Stoke-On-Trent | 2019 |
| I E Sustainability Limited | Stoke-On-Trent | 2019 |
| I Flame Limited | London | 2010 |
| I G H GAS & Heating Specialist Ltd | Hemel Hempstead | 2018 |
| I G S Property Management Limited | Bury | 1995 |
| I Griffin Ltd | Fleet | 2009 |
| I J Tarrant Limited | Basingstoke | 2008 |
| I Power Generation Limited | Stockport | 2015 |
| I Power Global P1 Limited | Stockport | 2025 |
| I Want Cheap Energy Ltd | Ashford | 2015 |
| I-Flow Technologies Ltd | Bromsgrove | 2023 |
| I-Hv Limited | Maidstone | 2019 |
| I-Novus Consultancy Ltd | Arbroath | 2015 |
| I-Novus Counselling Ltd | Arbroath | 2017 |
| I-Solar Investment Limited | London | 2010 |
| I.N.S. Air Conditioning Limited | Middlesex | 2007 |
| Iagree Solar UK Limited | Waterlooville | 2024 |
| IAM Utilities Limited | Oldham | 2016 |
| Iane Limited | Leeds | 2003 |
| IB Energy Ltd | Omagh | 2011 |
| IBE Airtnoch Limited | Chester Le Street | 2023 |
| IBE Carse Limited | County Durham | 2023 |
| IBE Flushdyke Limited | Chester Le Street | 2022 |
| IBE Haine Limited | County Durham | 2024 |
| IBE Hixons Limited | County Durham | 2024 |
| IBE Horse Leys Limited | County Durham | 2024 |
| IBE Kirkby Limited | Chester Le Street | 2024 |
| IBE LOW Common Limited | Chester Le Street | 2025 |
| IBE Lower Elker Limited | Chester Le Street | 2024 |
| IBE MID Hartwood Limited | County Durham | 2023 |
| IBE Mount Farm Limited | Chester Le Street | 2023 |