| MAD COW Cabs Ltd | Transport & logistics | 2025 |
| Maddison Water Technology Limited | Construction | 2006 |
| Made in Boston Ltd | Professional & scientific | 2020 |
| Magic Staff Ltd | Information & communication | 2019 |
| Magnum Enterprises (UK) Ltd | Financial services | 2016 |
| Magnum Fabrications Limited | Manufacturing | 2003 |
| Magnum Inns Ltd | Hospitality | 2016 |
| Magnum Mezzanine Floors Ltd | Manufacturing | 2008 |
| Mahon Lettings Ltd | Construction | 2022 |
| Main Ridge 2023 Limited | Hospitality | 2023 |
| Main Road (Stickney) Management Company Limited | Households | 2025 |
| Majickcare Ltd | Health & social care | 2016 |
| MAK & MAK Ltd | Other services | 2025 |
| MAK Haulage Limited | Transport & logistics | 2015 |
| Makaevo Kennels Ltd | Agriculture & fishing | 2022 |
| Makaylen Canine Services Ltd | Professional & scientific | 2025 |
| Make a Million Ltd | Transport & logistics | 2024 |
| Makolo Integrated Health Solutions Limited | Health & social care | 2025 |
| Makon Trans Ltd | Extraterritorial | 2018 |
| Malc Firth Landscapes Limited | Other services | 2009 |
| Malgorzata Lakomiec Ltd | Wholesale & retail | 2022 |
| Malik Locum Services Ltd | Health & social care | 2026 |
| Malinovskij Ltd | Transport & logistics | 2016 |
| Mammoth Recruitment and HR Services Ltd | Administrative & support | 2026 |
| Mango Professional Limited | Other services | 2012 |
| Mani Dents Ltd | Health & social care | 2019 |
| Manor Gate 2 Limited | Health & social care | 2020 |
| Manor Gate Care Ltd | Health & social care | 2020 |
| Manor Grange Financial Limited | Financial services | 2015 |
| Manor Maintenance Electrical Services Ltd | Construction | 2003 |
| Manorcourt Management Company (Skegness) Limited | Real estate | 2021 |
| Mantas Driving Limited | Transport & logistics | 2016 |
| Mantas&Spalnikas Limited | Transport & logistics | 2017 |
| Marbella Sun Ltd | Other services | 2022 |
| Margaritas Trades Limited | Wholesale & retail | 2026 |
| Maricare Investments (Trafford) Limited | Health & social care | 2023 |
| Marilise Jefferies Limited | Professional & scientific | 2010 |
| Marisol Sports Ltd | Wholesale & retail | 2025 |
| Mark Allen (Plumbing) Limited | Construction | 2000 |
| Mark Brewster Civils Ltd | Professional & scientific | 2015 |
| Mark Pocklington Transport Limited | Transport & logistics | 2012 |
| Mark Skipworth & SON Fabrications Limited | Manufacturing | 2021 |
| Mark Skipworth & SON Farming Ltd | Agriculture & fishing | 2022 |
| Mark Skipworth & SON Ltd | Agriculture & fishing | 2025 |
| Market Azadi Ltd | Wholesale & retail | 2025 |
| Market Place Lodge Limited | Real estate | 2024 |
| Marlee & SON Services Ltd | Construction | 2024 |
| Mars Employment Limited | Administrative & support | 2010 |
| Marsha Lane Auto Breakers Ltd | Wholesale & retail | 2025 |
| Marshlands (Lincolnshire) | Real estate | 1973 |
| Martech Engineering Solutions Ltd | Manufacturing | 2026 |
| Martyn Clarke Ltd | Hospitality | 2025 |
| Mary Property Rental Limited | Real estate | 2024 |
| Mastenbroek Environmental Limited | Wholesale & retail | 2017 |
| Mastenbroek Holding Company Limited | Professional & scientific | 1996 |
| Mastenbroek Limited | Manufacturing | 1973 |
| Matas Trans Ltd | Transport & logistics | 2017 |
| Matcas Investments Limited | Financial services | 2019 |
| Mates Estates Limited | Real estate | 2024 |
| Matt Cope Consulting Limited | Professional & scientific | 2016 |
| Matte Black Media Ltd | Professional & scientific | 2016 |
| Matteo Trans Ltd | Transport & logistics | 2019 |
| Matthewman Jewellers Limited | Wholesale & retail | 2024 |
| Matula Limited | Wholesale & retail | 2026 |
| Maude's the Jewellers Limited | Wholesale & retail | 2012 |
| Maudes On-Line Ltd | Wholesale & retail | 2020 |
| Maurick Property Services Limited | Real estate | 2005 |
| Maverick Automation Ltd | Manufacturing | 2010 |
| Maverick Automation Systems Limited | Professional & scientific | 2017 |
| Maxd Rive Haulage Ltd | Administrative & support | 2025 |
| MAY Developers Ltd | Construction | 2022 |
| Maycroft Limited | Wholesale & retail | 1981 |
| Mayhem Gym Ltd | Arts & recreation | 2022 |
| Maza Foods Limited | Wholesale & retail | 2024 |
| Mazak Ltd | Wholesale & retail | 2023 |
| MB Delivery Limited | Transport & logistics | 2019 |
| MB Rental Limited | Real estate | 2025 |
| Mbvm Transport Ltd | Transport & logistics | 2026 |
| Mccartney Food Service Limited | Wholesale & retail | 2013 |
| Mccoll's Contracting Limited | Manufacturing | 2021 |
| Mccreath Solutions Limited | Education | 2024 |
| Mcmark Detailing Peterborough Ltd | Administrative & support | 2025 |
| Mcmark Group Ltd | Administrative & support | 2026 |
| MD87 Services Ltd | Construction | 2022 |
| MDB Procurement Solutions Ltd | Professional & scientific | 2023 |
| MDH Electrical Limited | Construction | 2003 |
| MDM Cleaning Zone Ltd | Administrative & support | 2023 |
| MDS Property Group Ltd | Administrative & support | 2019 |
| Meadow Labs Limited | Information & communication | 2024 |
| Meadows Edge Care Home Limited | Health & social care | 2003 |
| Mechanical Electrical Services UK Ltd | Construction | 2026 |
| Medsmanagementuk Limited | Real estate | 2020 |
| Mel's Cleaning Services Ltd | Administrative & support | 2026 |
| Melody Trans Ltd | Transport & logistics | 2023 |
| Melwood Financial Services Limited | Professional & scientific | 2026 |
| MEM PAL Ltd | Transport & logistics | 2018 |
| Meno Academy Ltd | Education | 2023 |
| Mensa International Limited | Other services | 1965 |
| Mere Technical Services Ltd | Professional & scientific | 2013 |
| Merlin Engineering Company Halifax Limited | Real estate | 2011 |