| JCG Air Conditioning Limited | Ware | 2014 |
| JCM Golomoti UK Ltd | Reading | 2019 |
| JCM Salima UK Ltd | Reading | 2016 |
| Jcos Energy Limited | Kingsbridge | 2023 |
| JCT Electrical Technology Limited | Sheffield | 2012 |
| JD AD Limited | Lampeter | 2015 |
| JD Air Conditioning Ltd | Staines | 2023 |
| JDA Cooling Ltd | Glasgow | 2016 |
| JDA Engineering Solutions Ltd | Sunderland | 2017 |
| JDE Ventilation Systems Limited | Leeds | 2014 |
| Jdesk Ltd | Ayr | 2022 |
| JE Robinson Plumbing & Heating Ltd | Consett | 2006 |
| Jeffrey Kish Ltd | Sunderland | 2019 |
| Jellyfish Energy Limited | Newcastle Upon Tyne | 2014 |
| Jempower Limited | Bodmin | 2015 |
| Jenco Intl. Ltd | Carmarthen | 2011 |
| Jepiphany Limited | Cheltenham | 2023 |
| Jera NEX BP North East Limited | Sunbury On Thames | 2023 |
| Jerdon Energy Limited | London | 2017 |
| Jerriestown Solar Limited | London | 2025 |
| JES Electrical Services Ltd | Sidcup | 2017 |
| JET Ductwork Services Ltd | Dartford | 2014 |
| JET Renewables Limited | Halifax | 2009 |
| Jeyes Plumbing and Heating Limited | Northampton | 2014 |
| Jeyos Limited | Redcar | 2019 |
| JF Elec Ltd | Liverpool | 2020 |
| JF Electrical/Mechanical Limited | Leicester | 2010 |
| JF Utilities Limited | Welling | 2025 |
| JG Energy Services Ltd | Eastbourne | 2025 |
| JG Pears Grid Connection Limited | Sheffield | 2016 |
| JH Air Conditioning & Refrigeration Ltd | Bradford | 2020 |
| JH Air Conditioning Limited | Sutton Coldfield | 2023 |
| JH Renewables Ltd | Hexham | 2019 |
| JH Smart Trading Ltd | Romford | 2021 |
| JH Utilities Ltd | London | 2024 |
| JHK Renewable Energy Limited | Northallerton | 2025 |
| JHW Intelligent Electric Ltd | Beckenham | 2024 |
| Jiangsu Jingkeao Technology Co., Ltd | Gillingham | 2024 |
| Jiangsu Jingyan New Energy Technology Co., Ltd | Gillingham | 2024 |
| Jiangsu Jingyao New Energy Technology Co., Ltd | Gillingham | 2025 |
| Jiangsu JK Technology Co., Ltd | Gillingham | 2025 |
| Jiangsu JY New Energy Technology Co., Ltd | Gillingham | 2025 |
| Jiangsu JY Solar Technology Co., Ltd | Gillingham | 2024 |
| Jiangsu SLL Energy Co., Ltd | Gillingham | 2025 |
| Jigsaw Management Consultancy Ltd | Birmingham | 2017 |
| Jimmyps Ltd | Dartford | 2010 |
| Jinko Solar Co., Ltd | Gillingham | 2024 |
| Jipl Ltd | Birmingham | 2018 |
| Jishui Solar Ltd | Bristol | 2022 |
| Jj's Farm WT Ltd | Glasgow | 2013 |
| JJD Air-Conditioning Ltd | London | 2024 |
| JJJ Renewables Limited | Hayling Island | 2025 |
| JJL Associates Ltd | Leicester | 2001 |
| JJS 1 Limited | Stonehouse | 2023 |
| JJS 2 Limited | Stonehouse | 2023 |
| JJS 3 Limited | Stonehouse | 2023 |
| JJT Group Co., Limited | Beckenham | 2023 |
| JK Commercial, Mechanical & GAS Engineering Solutions Limited | Braintree | 2023 |
| JK Heating and Air CON Limited | Hounslow | 2019 |
| JKB Jointing Limited | Barrow In Furness | 2018 |
| Jleag AD Limited | London | 2020 |
| Jleag Solar 1 Limited | Macclesfield | 2015 |
| Jlewistrades Ltd | Norwich | 2019 |
| JLG Electrical Limited | Swansea | 2017 |
| JLG Electrical Services Ltd | East Boldon | 2018 |
| JLH Renewables Limited | Whaley Bridge | 2026 |
| JLW Plumbing & Heating Ltd | Malvern | 2023 |
| JLW Utilities Ltd. | Bishop Auckland | 2011 |
| JM Energy Services Ltd | Barnsley | 2024 |
| JM Specialist Services Ltd | Rickmansworth | 2011 |
| JMC Contracting Ltd | Sheffield | 2024 |
| JMC Hughes Limited | Betws Y Coed | 2024 |
| JMC Renewables IRL Ltd | Enniskillen | 2013 |
| JMD Turbine Limited | Omagh | 2016 |
| Jmjservices Limited | Bury St Edmunds | 2014 |
| JML Green Energy Limited | Hinckley | 2020 |
| JMN Utilities Limited | Romford | 2024 |
| JMW Energy Services Limited | Penarth | 2025 |
| JN Utility Services Ltd | Portsmouth | 2023 |
| JNC Energy Limited | Leicester | 2023 |
| JNH Electrical Limited | Chorley | 2019 |
| Jobs UK HR and PR Ltd | Birmingham | 2023 |
| Jobs UK Management Ltd | Birmingham | 2023 |
| Jockstown Energy Limited | Stockport | 2020 |
| Jocoda Holdings Ltd | Derry/Londonderry | 2025 |
| Joe's Generating Ltd | Edenbridge | 2018 |
| Joel and Jude Associates Limited | Camberley | 2015 |
| Joey Sparks Limited | London | 2025 |
| John a Green Offshore Ltd | Warrington | 2025 |
| John Brown Engineering Ltd | Ruislip | 2019 |
| John Byers Ltd | Stockton-On-Tees | 2024 |
| John Carr Consultancy Services Ltd | Preston | 2022 |
| John Churcher Electrical Ltd | Barry | 2011 |
| John Collier Ltd | Liverpool | 2003 |
| John Parry Electrical Limited | Beaconsfield | 2016 |
| Johnathan Fagan Ltd | Retford | 2013 |
| Johnny Campbell Ltd | Kilwinning | 2025 |
| Johnson & Phillips Limited | Newport | 2023 |
| Johnson Climate Solutions Ltd | Leicester | 2026 |
| Johnson Commissioning Services Limited | Doncaster | 2011 |