| Hutchinson Plant Services Limited | Newport | 2016 |
| Hutchison Energy Services Ltd | Strathpeffer | 2021 |
| Hutlog Ltd | Cheltenham | 2021 |
| Hvac & Refrigeration Engineering Limited | Aberdeen | 1999 |
| HWU Ltd | Dundee | 2024 |
| Hydarie OIL & GAS Ltd | Aberdeen | 2024 |
| Hyde Lane Holdings Limited | Chippenham | 2017 |
| Hydenlyne Limited | Wimborne | 2013 |
| Hydenlyne Projects Limited | Wimborne | 2013 |
| Hydrastone Ltd | Hartlepool | 2026 |
| Hydrawell UK Limited | Aberdeen | 2016 |
| Hydrocarbon Dynamics UK Limited | London | 2018 |
| Hydropos Offshore Limited | Exeter | 2018 |
| Hydroquest Enterprise Limited | Manchester | 2015 |
| Hygrade Resources Limited | London | 1990 |
| Hygrove Aggregates Limited | Swansea | 2021 |
| Hyline Energy UK Limited | Edgware | 2023 |
| Hymaroc Limited | London | 2025 |
| Hypermech Engineering Ltd | Nottingham | 2013 |
| Hyreach Offshore Ltd | Aberdeen | 2026 |
| I a & C Maciver Limited | Isle Of Lewis | 1993 |
| I B Marine Consultancy Ltd | Peterhead | 2020 |
| I L H Services Limited | Edinburgh | 2019 |
| I O E S Limited | London | 1998 |
| I&As (Insulation & Access Specialist) Limited | Saline | 2022 |
| I-Vigilant Technologies Limited | Aberdeen | 2012 |
| IAA Energy Resources Limited | London | 2018 |
| Iain Pllu Services Limited | Aberdeenshire | 2015 |
| Iain Rowell Ltd | Bonnyrigg | 2013 |
| Ialr Engineering Limited | Falmouth | 2012 |
| IAN J Robb Mechanical Ltd | Montrose | 2008 |
| IAN Kinge Logistics Ltd | Great Yarmouth | 2021 |
| IAN Lawson Electrical Ltd | Avoch | 2014 |
| IAN Youngman MMS Limited | Lowestoft | 2018 |
| Iapetus Energy Limited | Edinburgh | 2014 |
| Ibandula Business Cooperation Ltd | London | 2023 |
| Ibari Consult Ltd | London | 2025 |
| Iberian Mining Limited | Slough | 2005 |
| IC Exploration Limited | West Wickham | 2008 |
| ICC Consortium Limited | Westcliff-On-Sea | 2022 |
| Ice Business Services Ltd. | Edinburgh | 2011 |
| Icon Energy Limited | London | 1997 |
| ICS (2084) Limited | Lancaster | 2007 |
| Icsquared Limited | Aberdeen | 2017 |
| ICT Europe Ltd | Crieff | 2014 |
| Ictf Energy Limited | Cardiff | 2008 |
| ID Dawson Ltd | Ayr | 2025 |
| ID OIL Tools UK Ltd | Doncaster | 2022 |
| Idesa UK Limited | Chelmsford | 2019 |
| Idre Project Engineering Ltd | Eastbourne | 2015 |
| Idrill Limited | Stirling | 2003 |
| IG Paving Limited | London | 2017 |
| Igallc Ltd | Cambridge | 2022 |
| Igas Energy Development Limited | Lincoln | 2010 |
| Igas Energy Enterprise Limited | Lincoln | 2005 |
| Igas Energy Limited | Lincoln | 2004 |
| Igas Energy Production Limited | Edinburgh | 2006 |
| Igif Ltd | Aberdeen | 2018 |
| Ignus Resources Limited | London | 2025 |
| IGS (International Geoscience Services) Limited | Bingham | 2010 |
| IJB Services Ltd | Beccles | 2012 |
| Ikdn Ltd | Glasgow | 2021 |
| Iken Energy Limited | Teddington | 2017 |
| Ikmd Limited | Much Hadham | 2010 |
| Ilex Resources Limited | West Clandon | 2018 |
| ILR Construction Ltd | Dundee | 2026 |
| IM Inspection Services Limited | Isle Of Lewis | 2010 |
| Imachinery Ltd | Dewsbury | 2017 |
| Imaged Reality Ltd | London | 2016 |
| Imagineering Limited | Grimsby | 2007 |
| IMC Montan Limited | London | 2012 |
| Imec Subsea Ltd | Coventry | 2014 |
| Imenco UK Limited | Aberdeen | 2010 |
| Imerys Minerals Limited | Par | 1932 |
| IMH Technical Services Ltd | Peterhead | 2017 |
| IMI Offshore Lifting Ltd | Oban | 2025 |
| Imineval Ltd | Cardiff | 2023 |
| IMM Access and Inspection Services Ltd | Blackpool | 2018 |
| Impact Africa Limited | London | 2010 |
| Impact Energies International Limited | London | 2022 |
| Impact Energies Limited | London | 2026 |
| Impact OIL & GAS Limited | London | 2011 |
| Impact Selector Limited | Aberdeen | 1998 |
| Imperial Mining, Minerals and Chemicals Trading UK Ltd | London | 2010 |
| Importaciones Portugal Ltd | Cardiff | 2021 |
| IN Depth GAS Solutions Ltd | England | 2016 |
| IN One Place Trading Limited | London | 2020 |
| In-Grid Solutions Limited | London | 2020 |
| Inchgower GEO Limited | Middlesex | 2025 |
| Incor Investments Limited | London | 2018 |
| Independent Energy Limited | Lancing | 2019 |
| Independent Oilfield Inspection Limited | Aberdeenshire | 1993 |
| Indi-Pendent Plant Sales Limited | Derby | 2005 |
| Indigo Pumpkin Ltd | Weybridge | 2016 |
| Industrial Abseiling Services Ltd | Wallsend | 2025 |
| Ineng Limited | London | 2023 |
| Ineos 120 Exploration Limited | Lyndhurst | 2008 |
| Ineos Clipper South B Limited | Lyndhurst | 2003 |
| Ineos Clipper South C Limited | Lyndhurst | 2003 |
| Ineos E&P (Siri) UK Limited | Lyndhurst | 1991 |