| Gulf International Minerals Limited | Kent | 2010 |
| Gulf Interstate Engineering (U.K.) Limited | London | 1985 |
| Gulf Marine Subsea Services Limited | Salford | 2025 |
| Gulfsands Energy UK Limited | London | 2025 |
| Gulfsands Petroleum PLC | London | 2004 |
| Gulfstream Services International UK Limited | Aberdeen | 2009 |
| Gunn Technical Services Limited | Wick | 2014 |
| Gunn-Bbl Energy Services Ltd | London | 2020 |
| Gusmaintain Ltd | Irvine | 2021 |
| GUT4 Ltd | Lochwinnoch | 2023 |
| Guus Investments Co. Ltd | London | 2020 |
| GUY Chalmers Rigging Ltd | Ayr | 2015 |
| Guyana Deep Water II UK Limited | London | 2018 |
| Guyana Deep Water III UK Limited | London | 2019 |
| Guyana Deep Water Operations UK Limited | London | 2016 |
| Guyana Deep Water UK Limited | London | 2016 |
| GW Access Limited | Motherwell | 2013 |
| GWM Operations Limited | London | 2013 |
| Gy-Dw-Uk-Iv Limited | London | 2021 |
| H and K Enterprises Limited | Haddington | 1987 |
| H B Mines Limited | London | 2017 |
| H G Crushing Limited | Huddersfield | 2013 |
| H M Research Associates Limited | Loughborough | 2000 |
| H O North East Ltd | Darlington | 2016 |
| H Technical Resources Limited | Durham | 2012 |
| H. V. Bowen & Sons (Quarry) Ltd | Derby | 2011 |
| H.J. Banks and Company Limited | Durham | 1976 |
| H.T.S NE Ltd | North Shields | 2017 |
| H.Tuckwell & Sons Limited | Abingdon | 1922 |
| H2 Energy Advisors Limited | London | 2023 |
| H2 Petroleum Consulting Ltd | Nottingham | 2014 |
| H2O Proservices UK Ltd | London | 2026 |
| H2OIL Limited | Great Yarmouth | 2019 |
| H41G Ltd | London | 2014 |
| Hadar Global Ltd | Wednesbury | 2018 |
| Hades Oilfield Products Limited | London | 2011 |
| Hadley's Offshore Supply Limited | London | 2012 |
| Hadspen Quarry Ltd | Hadspen | 2003 |
| Haghkar Offshore Limited | Ashington | 2014 |
| Hale Mining Company Limited | London | 2026 |
| Halifax Energy Group Limited | Barking | 2010 |
| Halite Global Ltd | Manchester | 2013 |
| Hall Construction Services Limited | Rushyford | 1986 |
| Hallam Geoscience Limited | Sheffield | 2022 |
| Halley Access & Rigging Ltd | Leven | 2026 |
| Halliard Consulting Ltd | Edinburgh | 2013 |
| Halliburton Limited | London | 1970 |
| Halliburton Manufacturing and Services Limited | London | 1958 |
| Halliday Mechanical Site Services Limited | Bathgate | 2019 |
| Halliday MPD Services Ltd | Lowestoft | 2025 |
| Hallyards Handling Limited | Prestwick | 2008 |
| Halo Minerals PLC | London | 2007 |
| Halyard Offshore Limited | London | 1976 |
| HAM & Doulting Stone Co Limited | Somerton | 2004 |
| Hamak Strategy (UK) Limited | London | 2026 |
| Hamarr Limited | Balgownie Road, Bridge Of Don | 2023 |
| Hamba Lapa Ltd | Swindon | 2026 |
| Hamilton (Sales & Lettings) Limited | | 1997 |
| Hamilton Engineering & Safety Limited | Morpeth | 2012 |
| Hamirah Services Limited | Camberley | 1999 |
| Hamish Lloyd Limited | Dundee | 2025 |
| Hamnavoe OIL Services Limited | Motherwell | 2025 |
| Hampton Petroleum Development Limited | Basingstoke | 2003 |
| Hanbeck (Drystone) Limited | Sleaford | 2021 |
| Hancox Well Services Ltd | Montrose | 2010 |
| Hangzhou Yunyu Scientific Instrument Co., Ltd. | Beckenham | 2025 |
| Hannon Westwood Holdings Limited | Edinburgh | 2009 |
| Hanover (UK) Marine Biotechnology Limited | Beckenham | 2024 |
| Hansa Hydrocarbons Limited | Reading | 2007 |
| Hanson Aggregates Marine Limited | Maidenhead | 1950 |
| Hanson Quarry Products Europe Limited | Maidenhead | 1935 |
| Happ Technology Ltd | Falmouth | 2007 |
| Harbour Energy Argentina Limited | London | 2023 |
| Harbour Energy Central Andaman Limited | London | 2013 |
| Harbour Energy Finance Limited | London | 2016 |
| Harbour Energy Marketing Limited | London | 2018 |
| Harbour Energy Services Limited | London | 2017 |
| Hard Rock Mining Limited | Sheffield | 2016 |
| Harden Redstone Company Limited | Newcastle Upon Tyne | 1957 |
| Hargreaves (North West) Limited | Leyland | 2009 |
| Hargreaves ASH Marketing Limited | Dewsbury | 2008 |
| Hargreaves Roadstone Limited | Dewsbury | 2008 |
| Harlequin Energy Limited | London | 2020 |
| Harleyford Aggregates Limited | Marlow | 1964 |
| Harleyford Valley Limited | Harlow | 2012 |
| Harlow Hiedra Engineering Services Limited | Kilmacolm | 2018 |
| Harmston Waste Management Limited | Lincoln | 2001 |
| Harnfield Properties Limited | Grantham | 1999 |
| Harranna Ltd | Montrose | 2006 |
| Harrel Oilfield Services Ltd | Aberdeen | 2018 |
| Harris Geoconsult Limited | Bristol | 2011 |
| Harrison Operations Ltd | Grimsby | 2023 |
| Harrison Rigging Services Limited | Plymouth | 2018 |
| Harrop Edge Quarry Ltd | Cheadle Hulme | 2015 |
| Harta Global Energy Limited | London | 2023 |
| Hartham Park Bath Stone Limited | Cheltenham | 2014 |
| Hartshead Resources Ltd | Brighton | 2019 |
| Hartwell Petroleum Ltd. | Aberdeen | 2005 |
| Harvex Geosolutions Limited | London | 2009 |
| Harwood Quarry Company Limited | Warrington | 1938 |