| M.Pg.Cars Limited | Information & communication | 2026 |
| M.R Decorating Ltd | Construction | 2026 |
| M.R. Site Services (Barnsley) Limited | Construction | 2013 |
| M.R.C.Distribution Limited | Administrative & support | 2015 |
| M.S.D (Yorkshire) Ltd | Real estate | 2025 |
| M.Thistlewood Construction Services Limited | Construction | 2014 |
| M27 Ltd | Wholesale & retail | 2025 |
| M4 Electrical Solutions Ltd | Construction | 2023 |
| M@A Trade Cars Ltd | Wholesale & retail | 2022 |
| MAB 20 Ltd | Hospitality | 2025 |
| MAB Removal Services Ltd | Water & waste | 2018 |
| Mabelcyd | Financial services | 2025 |
| MAC Tools (Barnsley) Limited | Wholesale & retail | 2003 |
| Mach Rubber Limited | Manufacturing | 2018 |
| MACH1 Controls Ltd | Information & communication | 2026 |
| Macleod Pipework Engineering Limited | Professional & scientific | 2013 |
| MAD Hatters Lunchbox Ltd | Hospitality | 2026 |
| MAD Metals Ltd | Wholesale & retail | 2025 |
| Madalin Courier Limited | Transport & logistics | 2017 |
| Made Build Ltd | Professional & scientific | 2026 |
| Made by Golden Ltd | Other services | 2016 |
| Madp.Uk Ltd | Information & communication | 2016 |
| Mady Auto Ltd | Wholesale & retail | 2020 |
| MAE Tech (UK) Limited | Information & communication | 2013 |
| Maenga Investments Ltd | Real estate | 2024 |
| Maezy Radiology Solutions Limited | Health & social care | 2023 |
| Magic Jellyfish Limited | Professional & scientific | 2018 |
| Magic Kerala Holidays Ltd | Administrative & support | 2026 |
| Magic Kerala Spirits UK Ltd | Wholesale & retail | 2026 |
| Magic of Currys Ltd | Hospitality | 2019 |
| Magical Moments Gift Stores Ltd | Wholesale & retail | 2019 |
| Magna Colours Holdings Limited | Professional & scientific | 2009 |
| Magna Colours Limited | Manufacturing | 1978 |
| Magnacool Ltd | Extraterritorial | 2019 |
| Magnihire Limited | Administrative & support | 2026 |
| Mailaris Ltd | Hospitality | 2022 |
| Mainstream Solutions Ltd | Administrative & support | 2024 |
| Maisha Worsbrough Ltd | Hospitality | 2026 |
| Maison DU Biere (Elsecar) Limited | Wholesale & retail | 2018 |
| Majic Makers Ltd | Wholesale & retail | 2021 |
| Majo Holdings Limited | Professional & scientific | 2020 |
| Makatulives Limited | Health & social care | 2022 |
| Makey Group Limited | Information & communication | 2026 |
| Malibu Homes Limited | Real estate | 2019 |
| Malibu Property Ltd | Real estate | 2024 |
| Mallinson & Co Estates Limited | Real estate | 2021 |
| Mallinson Consultancy Services Limited | Professional & scientific | 2025 |
| Mallinson Developments Limited | Real estate | 2025 |
| Mallinson Garages Limited | Wholesale & retail | 2025 |
| Mallinson Properties Limited | Real estate | 2017 |
| Mallinson Warehousing & Storage Limited | Transport & logistics | 2025 |
| Mals Holdings Limited | Transport & logistics | 2020 |
| Maltby Car and Commercial Limited | Wholesale & retail | 2024 |
| Mama Castleford Ltd | Hospitality | 2024 |
| Mana Healthcare Ltd | Public administration | 2025 |
| Mandafoods Limited | Manufacturing | 2004 |
| Mane Metering Services Limited | Other services | 2017 |
| Manor Court Management Company (Barnsley) Limited | Households | 2013 |
| Manor Court Number One Management Company Limited | Households | 2006 |
| Manor Kennels Limited | Other services | 2022 |
| Mansfield Colliery Miners Welfare Social Club Limited | Other services | 1991 |
| Mansion Grange Limited | Real estate | 1982 |
| Mansion House Hartlepool RTM Company Limited | Households | 2025 |
| Manterfield Building & Roofing Limited | Construction | 2013 |
| Manterfield Properties Limited | Real estate | 2018 |
| Manvers Automotive Repair Specialist Ltd | Wholesale & retail | 2015 |
| Manvers Engineering Limited | Manufacturing | 1996 |
| Manx Arms Barnsley Ltd | Hospitality | 2024 |
| MAP & Find Ltd | Real estate | 2026 |
| MAP Caring Services Limited | Health & social care | 2019 |
| Maple Estates (Barnsley) Limited | Real estate | 1975 |
| Mapplewell & Staincross Village Hall (Trading) Ltd | Hospitality | 2006 |
| Mapplewell and Staincross Village Hall Limited | Health & social care | 2005 |
| Mapplewell Bottle Shop Ltd | Wholesale & retail | 2019 |
| Mapplewell Meadows Farm Ltd | Real estate | 2023 |
| Mara Telecoms Ltd | Manufacturing | 2012 |
| Marble Salon Limited | Other services | 2020 |
| Marc Wilmot Limited | Professional & scientific | 2017 |
| March Tank Construction Ltd | Construction | 2010 |
| Marchelena Transport Ltd | Transport & logistics | 2016 |
| Marching Drums United Kingdom Limited | Wholesale & retail | 2012 |
| Marcus Jones Property Limited | Construction | 2018 |
| Margaret Court Management Company (Wombwell) Limited | Professional & scientific | 2004 |
| Marie's Sparkle Clean Limited | Administrative & support | 2026 |
| Marinel Trans Limited | Transport & logistics | 2021 |
| Mario Truck Transport Ltd | Transport & logistics | 2017 |
| Mariusbondoret Limited | Construction | 2022 |
| Marjenterprise Ltd | Hospitality | 2026 |
| Marjorie Marigold Limited | Professional & scientific | 2026 |
| Mark 5 Limited | Professional & scientific | 2023 |
| Mark Attwood Productions Ltd | Information & communication | 2017 |
| Mark Broadhurst Ltd. | Information & communication | 2017 |
| Mark Coulson Ltd | Transport & logistics | 2025 |
| Mark Gill Financial Services Ltd | Financial services | 2012 |
| Mark Latham Limited | Professional & scientific | 2012 |
| Mark Lawton Limited | Agriculture & fishing | 2006 |
| Mark Todd Services Limited | Construction | 2014 |
| Markate Properties Limited | Real estate | 2025 |
| Markclean Hygiene Services Limited | Administrative & support | 2008 |
| Marker Developments Limited | Manufacturing | 2025 |