| M&J Property Ventures Ltd | Real estate | 2025 |
| M&J York Limited | Hospitality | 2021 |
| M&L Lawson Transport Ltd | Transport & logistics | 2013 |
| M&M Landscapes Ltd | Administrative & support | 2002 |
| M&M Parks Limited | Hospitality | 2026 |
| M&N Casey Developments Limited | Real estate | 2022 |
| M&N Rodgers & Sons Limited | Real estate | 2002 |
| M&W Stays Ltd | Real estate | 2025 |
| M. & a. Wright Construction Ltd. | Construction | 2003 |
| M. G. Maltby Limited | Construction | 1996 |
| M. Silversides & SON Limited | Transport & logistics | 2003 |
| M. Smith Investments Ltd | Real estate | 2023 |
| M.Brittain(York)Limited | Manufacturing | 1972 |
| M.E. Willis (Sales & Hire) Limited | Wholesale & retail | 1982 |
| M.F Kitchens Limited | Construction | 2026 |
| M.G. Pocock (Surveyors) Limited | Administrative & support | 1995 |
| M.J.Berry Ltd | Manufacturing | 2018 |
| M.Moore & Sons Ltd | Manufacturing | 2012 |
| M.P.H. Inspection Services Limited | Professional & scientific | 2002 |
| M.P.H. Properties (York) Limited | Real estate | 2017 |
| M.R.Bailey Ltd | Professional & scientific | 2014 |
| M.U.S.C Limited | Professional & scientific | 2022 |
| M.Y.D Supplies Ltd | Manufacturing | 2017 |
| M300 Limited | Financial services | 2025 |
| M4 UK Limited | Manufacturing | 2002 |
| M4G1C | Financial services | 2020 |
| MA Maison Interiors Limited | Wholesale & retail | 2020 |
| Mabel Property Ltd | Real estate | 2016 |
| Maboa Solutions Ltd | Information & communication | 2022 |
| Mabp Ltd | Real estate | 2019 |
| Mabv Ltd | Administrative & support | 2020 |
| MAC & Mabel's London Ltd | Other services | 2014 |
| MAC 17 Consulting Ltd | Information & communication | 2024 |
| MAC 4D Limited | Professional & scientific | 2025 |
| MAC Conveyancing Services Limited | Professional & scientific | 2022 |
| MAC Property Limited | Real estate | 2008 |
| Mac-Serve Ltd | Construction | 2012 |
| Macd Ltd | Administrative & support | 2025 |
| Macdonald Alveston Limited | Hospitality | 2006 |
| Macdonald Bear Limited | Hospitality | 2006 |
| Macdonald Berystede Limited | Hospitality | 2006 |
| Macdonald Blossoms Limited | Hospitality | 2006 |
| Macdonald Botley Park Limited | Hospitality | 2006 |
| Macdonald Compleat Angler Limited | Hospitality | 2006 |
| Macdonald Crutherland Limited | Hospitality | 2006 |
| Macdonald Dona Lola NO.1 Limited | Arts & recreation | 1987 |
| Macdonald Frimley Hall Limited | Hospitality | 2006 |
| Macdonald Houstoun House Limited | Hospitality | 2006 |
| Macdonald Inchyra Grange Limited | Hospitality | 2006 |
| Macdonald Kilhey Court Limited | Hospitality | 2006 |
| Macdonald Leeming House Limited | Hospitality | 2006 |
| Macdonald Loch Rannoch Limited | Professional & scientific | 1965 |
| Macdonald Tickled Trout Limited | Hospitality | 2006 |
| Macdonald Travel Club Limited | Professional & scientific | 1988 |
| Macdonalds (York) Limited | Real estate | 1947 |
| Macdougal LEA Ltd | Construction | 2006 |
| Maced Face Records Ltd | Arts & recreation | 2024 |
| Macey Property Consultancy Limited | Construction | 2003 |
| Macfadyen Holdings Ltd | Financial services | 2021 |
| Machinenergy Ltd | Manufacturing | 2014 |
| Machines Automation Robotic Systems Ltd | Manufacturing | 1984 |
| Macintosh Contractors Ltd | Construction | 2025 |
| Mack 1 Cable Jointing Services Limited | Construction | 2015 |
| Mackenzie & Mackenzie Limited | Financial services | 2025 |
| Macro Milk Ltd | Manufacturing | 2025 |
| MAD About Electrics Limited | Construction | 2010 |
| MAD About Property Limited | Construction | 2013 |
| MAD Alice 21 Ltd | Real estate | 2021 |
| Mad-Maxx Valeting Ltd | Administrative & support | 2019 |
| Maddy Ruff Ltd | Professional & scientific | 2020 |
| Made by Mouse Limited | Manufacturing | 2019 |
| Made in Ebor Ltd | Information & communication | 2013 |
| Made in Oldstead Ltd | Manufacturing | 2020 |
| Made in Yorkshire Limited | Other services | 2000 |
| Made in Yorkshire Trading Limited | Administrative & support | 2017 |
| Madhyamaka Kadampa Meditation Centre Ltd | Other services | 1980 |
| MAE Cafe Ltd | Hospitality | 2025 |
| Maes Dyfed Management Company Limited | Households | 2013 |
| Maes Glas Vets Limited | Professional & scientific | 2014 |
| Maes Y Parc (Cross Hands) Management Company Limited | Households | 2015 |
| Maes Y Rhos (Ystradgynlais) Management Company Limited | Households | 2023 |
| Magellan Design Limited | Professional & scientific | 2000 |
| Magequal Limited | | 1985 |
| Maggie Clean Ltd | Administrative & support | 2023 |
| Magic Hatter Entertainments Ltd | Arts & recreation | 2010 |
| Magicvolcano Ltd | Hospitality | 2013 |
| Magium Commerce Limited | Information & communication | 2014 |
| Magniflux Limited | Health & social care | 2024 |
| Magnum Equipment Ltd | Manufacturing | 2012 |
| Magnum Homes Ltd | Real estate | 2025 |
| Magnus Design Build Limited | Extraterritorial | 1988 |
| Magnus Holdings Limited | Extraterritorial | 1988 |
| Maia Dental Limited | Health & social care | 2020 |
| Maia Property Holdings Limited | Real estate | 2026 |
| Maiara Consulting Limited | Professional & scientific | 2024 |
| Maidle Limited | Professional & scientific | 2024 |
| Mailboxuk.Com Ltd | Other services | 2024 |
| Main Avenue Management Limited | Administrative & support | 1988 |
| Main Realisations Limited | Information & communication | 2006 |
| Mainprize Developments Limited | Real estate | 2021 |