| M.K.S Maintenance Ltd | Cardiff | 2020 |
| M.Nixon Services Ltd | London | 2026 |
| M.R.W Electrical & Security Limited | Basildon | 2023 |
| M.S Offshore Services Ltd | Wirral | 2023 |
| M.T Renewables Ltd. | Magherafelt | 2016 |
| M.Z.J. Ltd | Unst | 2018 |
| M0 Liquidity on Demand Limited | Oldham | 2019 |
| M29 Ltd | Kirk Hammerton | 2010 |
| M2J Group Limited | Ellesmere Port | 2024 |
| M40 LPG Ltd | High Wycombe | 2025 |
| M7 Utilities Ltd | Buntingford | 2024 |
| M7 Ventilation Ltd | Brentwood | 2024 |
| MA Energy Limited | London | 2008 |
| MA020 Limited | Truro | 2014 |
| MAA Energy Ltd | Uxbridge | 2025 |
| Maac.Tech Engineering Limited | Ashington | 2025 |
| Mabilla Energy & Metals Ltd | Harlow, Essex, England | 2012 |
| Mablethorpe Green Energy Centre Limited | Faversham | 2021 |
| Mablethorpe NG Limited | Cheltenham | 2023 |
| Mablethorpe Wind Park Limited | Stroud | 2000 |
| Mabo Refrigeration Ltd | Guisborough | 2019 |
| MAC Generation Limited | Staveley | 2017 |
| Macdonald Design Services Ltd | Dundee | 2019 |
| Macdonald Wind Ltd | Point | 2013 |
| Macee Group Ltd | Holmfirth | 2026 |
| Macenergie Limited | Whitchurch | 2011 |
| Macfas Ltd | Cardiff | 2023 |
| Mach Power Limited | Antrim | 2013 |
| Machaire Energy Storage Limited | Kings Langley | 2024 |
| Machairwind Limited | Glasgow | 2022 |
| Macht Limited | London | 2020 |
| Mackie Plumbing and Heating Limited | Bridge Of Weir | 2019 |
| Mackie's Renewables Limited | Rothienorman | 2020 |
| Mackwood International Ltd | London | 2023 |
| Macmillan D C Limited | Edinburgh | 2019 |
| Macmillan Power Limited | Bridgend | 2013 |
| Macpherson Renewables Limited | Forfar | 2025 |
| Macr Ltd | Nottingham | 2015 |
| Macro Access Ltd | Launceston | 2022 |
| Macs Power Engineering Ltd | St. Helens | 2016 |
| Macspower Limited | Great Yarmouth | 2018 |
| Madame Carle Limited | Dungannon | 2013 |
| Maddan Wind Ltd | Belfast | 2017 |
| Madjeston Renewable Energy Limited | Reading | 2022 |
| Maerdy Windfarm Limited | London | 2008 |
| Maes Elwy Hydro Limited | Caernarfon | 2013 |
| Maesmawr Renewables Ltd | Llanidloes | 2015 |
| Maesnant Energy Park Limited | Cardiff | 2021 |
| Maghaberry Solar Limited | London | 2013 |
| Maghera Green Energy Limited | Belfast | 2020 |
| Magherafelt BES Ltd | Lisburn | 2022 |
| Magherakeel Wind Farm Limited | Cookstown | 2018 |
| Magheralin Energy Limited | Larne | 2022 |
| Magheralone Energy Limited | Ballynahinch | 2016 |
| Magheramore Energy Limited | Larne | 2022 |
| Magic Engineering Ltd | Weymouth | 2018 |
| Magnify Capital Ltd | London | 2025 |
| Magnora Offshore Wind Holding Limited | Edinburgh | 2021 |
| Magnora Offshore Wind N3 Limited | Aberdeen | 2021 |
| Magor NET Zero Ltd | London | 2021 |
| Maguire Energy Limited | Ballymena | 2013 |
| MAH Electrical Contractors Limited | Weymouth | 2010 |
| Maher Traders Ltd | Stockport | 2022 |
| Mahuika Limited | Walton-On-Thames | 2016 |
| Maiden Head Energy Limited | Exeter | 2024 |
| Maidenhead West Power Limited | London | 2019 |
| Main Sunny Limited | Edinburgh | 2023 |
| Maine FM Ltd | Consett | 2025 |
| Maine One Limited | Newcastle Upon Tyne | 2025 |
| Mainstay Utilities Ltd | Manchester | 2013 |
| Maintenance & Plumbing Ltd | Borehamwood | 2016 |
| MAINY10 Electrical Services Limited | West Malling | 2017 |
| Mair Wind Limited | Turriff | 2015 |
| Maisemore Court Farm Energy Centre Limited | Rochford | 2020 |
| Majors Hill Solar Limited | London | 2015 |
| Majr Limited | Bury St Edmunds | 2013 |
| Make HAY Solar Installers Ltd | Southampton | 2011 |
| Makenny Wind Ltd | Belfast | 2016 |
| Makrogama Ltd | Wisbech | 2021 |
| MAL Tool & Engineering Limited | Burnley | 1985 |
| Malaby Biogas Limited | Wellingborough | 2009 |
| Malakoff and WM. Moore Limited | Aberdeen | 1973 |
| Malatovia Ltd | London | 2024 |
| Maldon Power Group Ltd | Basildon | 2026 |
| Maldon Wycke Solar Farm Limited | London | 2020 |
| Maleo Energy Limited | London | 2017 |
| Malfi Electric Ltd | Harrow | 2026 |
| Malihah Living Ltd | Bolton | 2025 |
| Malin Sea Wind Limited | London | 2023 |
| Mallard Pass Solar Farm Limited | London | 2020 |
| Mallory Energy Ltd | Manchester | 2017 |
| Malmesbury Solar Limited | London | 2006 |
| Malmpit Solar Limited | Cardiff | 2010 |
| Maluda Limited | York | 2014 |
| Malwine Solar SPV 1 Ltd | London | 2014 |
| Mamhilad Solar Limited | London | 2018 |
| Mams Engineering Ltd | Glasgow | 2024 |
| MAN Innovations Limited | Aberdeen | 2017 |
| Manachainn Rois Green Energy Limited | London | 2022 |
| Mancala Guarantors Ltd | Liverpool | 2022 |