| JM Hutt Services Limited | Dundee | 2013 |
| JM Integrity Services Ltd | Ashington | 2023 |
| JM Quarry Services Ltd | Pontypool | 2018 |
| JMB Concepts Limited | Cardiff | 2018 |
| JMC Engineering (UK) Limited | Eastwood | 1992 |
| JMC Renewable Solutions Ltd | Stockton-On-Tees | 2018 |
| Jmcguire Ltd | Stirling | 2023 |
| JME Fleet Assist Ltd | Airdrie | 2021 |
| Jmea Solutions Ltd | Glasgow | 2024 |
| Jmlb Inspection Ltd. | Cowdenbeath | 2011 |
| JMP Aggregates Ltd | Gravesend | 2021 |
| JMX Ventures Limited | London | 2023 |
| JNP Engineering and Projects Ltd | Linlithgow | 2015 |
| Joash Limited | Scarborough | 2012 |
| Jobo Ropes Ltd | Norwich | 2026 |
| Jobs UK Armagh Ltd | Birmingham | 2023 |
| Jobs UK Glasgow Ltd | Birmingham | 2023 |
| Jobs UK Lisburn Ltd | Birmingham | 2023 |
| Jobs UK Londonderry Ltd | Birmingham | 2023 |
| Jobs UK Newry Ltd | Birmingham | 2023 |
| Jobs UK South Gloucestershire Ltd | Birmingham | 2023 |
| Jobs UK Telford and Wrekin Ltd | Birmingham | 2023 |
| Jobs UK Worcestershire Ltd | Birmingham | 2023 |
| Joch Consulting Limited | Leigh | 2017 |
| John Brewster Limited | Swanage | 2003 |
| John Butler (Aberdeen) Ltd. | | 1996 |
| John Cook Pipework Services Ltd | Stockton-On-Tees | 2017 |
| John Crane Asset Management Solutions Limited | Aberdeen | 1997 |
| John Fitzpatrick Ltd | York | 2009 |
| John Hancock & Sons (Bath) Limited | Bath | 1982 |
| John Jackson Services Ltd | Newcastle Upon Tyne | 2019 |
| John Kernaghan and Associates Limited | Berks | 1989 |
| John Luscombe & Co. Limited | Oxford | 2018 |
| John Maclachlan (Quarries) Limited | Oban | 1985 |
| John O'Donnell Mining Limited | Gorton | 2011 |
| John Price and Partners Ltd | London | 2017 |
| John Quinn Services Ltd | London | 2026 |
| John Spencer Wellsite Geological Consultancy Limited | Newcastle Upon Tyne | 2008 |
| John Underwood Consulting (Kent) Limited | Ashford | 1997 |
| John Wainwright & Co. Limited | Radstock | 1902 |
| Johnathon Phillips Services Ltd | Buxton | 2012 |
| Johnson & Steller Limited | London | 2014 |
| Johnsons (Chopwell) Limited | Belper | 1941 |
| Johnsons Wellfield Ltd | Huddersfield | 1943 |
| Johnston Quarry Group Limited | Chipping Norton | 2007 |
| Jolunari Limited | Inverurie | 2021 |
| JON Dixon Electrical Services Ltd | Poulton-Le-Fylde | 2012 |
| Jones OIL & GAS Services Ltd | East Boldon | 2012 |
| Jordan Rose Ltd | South Shields | 2012 |
| Jordans Quarries Ltd | Omagh | 2025 |
| Jose Consulting U.K Ltd | Southall | 2019 |
| Joseph Arnold & Sons Limited | Leighton Buzzard | 1993 |
| Joseph Kimberley & Sons Limited | Chester | 1961 |
| Josey Global Limited | Swansea | 2026 |
| Josiah Paull DIW Limited | Coulsdon | 2026 |
| Josiah Paull Onen Limited | Coulsdon | 2026 |
| Joss (Aberdeen) Limited | Aberdeen | 1934 |
| Joss Production Services Ltd | Montrose | 2017 |
| Jpci Ltd | Stockton-On-Tees | 2026 |
| JPE Well Engineering Ltd | Montrose | 2013 |
| JPH Energy Limited | Great Yarmouth | 2023 |
| JPJ Constuction & Engineering Ltd | Liverpool | 2018 |
| JPM Inspections Limited | Whitley Bay | 2014 |
| JR Energy Consulting Limited | Henley | 2016 |
| JR Subsea Ltd | Aberdeen | 2009 |
| Jrsh Onshore Ltd | Great Yarmouth | 2024 |
| JSA Electrical Ltd | Hartlepool | 2015 |
| JSB Energy Partners Limited | London | 2017 |
| JSC Jurassic Salt Co Ltd | Swanage | 2023 |
| JT Offshore Services Ltd | Great Yarmouth | 2021 |
| JTB Design Services Ltd | Linlithgow | 2016 |
| Jtec Equipment Limited | Pontyclun | 2016 |
| Jtec Machinery Ltd | Pontypridd | 2019 |
| Jtenk Group Company Limited | London | 2025 |
| JTH Services Ltd | Glasgow | 2018 |
| JTW Inspections Ltd | Wallsend | 2023 |
| Jubilee Metals Group PLC | London | 2002 |
| Juniper (NO. 7) Limited | 29 Wellington Street | 1991 |
| Juno Mining Consultants Ltd | Bucknell | 2018 |
| Jupiter Lithium Limited | Weybridge | 2023 |
| Jurassic Subsea Ltd | Budleigh Salterton | 2020 |
| Jurassica OIL & GAS Ltd | Surbiton | 2006 |
| Just GAS Services Ltd | Croydon | 2024 |
| Justphils Limited | Ashford | 2024 |
| Juwon Tankers UK Limited | London | 2018 |
| JVE Well Services Ltd | Montrose | 2011 |
| JVK Engserv Ltd | Aberdeen | 2016 |
| JW Cementing Services Ltd | Glasgow | 2019 |
| JW Inspections Limited | Kinlochbervie | 2016 |
| JW Safety NE Ltd | London | 2019 |
| Jwae Limited | Whitby | 2013 |
| Jwminconsult Limited | Huntingdon | 2013 |
| JWR Solutions Ltd | Great Yarmouth | 2024 |
| Jz.Ndt Inspection Ltd | Aberdeen | 2019 |
| K & a Engineering Services Limited | Durham | 2016 |
| K & J Knight Tunnelling Ltd | Portsmouth | 2013 |
| K C Subsea Services Ltd | Preston | 2024 |
| K D K Well Services Limited | Montrose | 2008 |
| K E Lunness Limited | Doncaster | 2022 |
| K E Offshore Limited | Newcastle Upon Tyne | 2019 |