| Mary the Great Ltd | Wholesale & retail | 2018 |
| Maryo&Marin Trans Ltd | Transport & logistics | 2023 |
| Mason Baggott and Garton Solicitors Limited | Professional & scientific | 2021 |
| Mason Milner Ltd | Professional & scientific | 2017 |
| Masstransport Ltd | Transport & logistics | 2023 |
| Masters Medical Services Limited | Health & social care | 2017 |
| Masy Care Limited | Health & social care | 2021 |
| Matias Direct Ltd | Transport & logistics | 2025 |
| Matisa(U.K.)Limited | Wholesale & retail | 1964 |
| Matkai Ltd | Transport & logistics | 2023 |
| Matt Thompson Plumbing Contractors Limited | Construction | 2020 |
| Matte Black Properties Limited | Real estate | 2025 |
| Matte Black Surfacing Limited | Construction | 2020 |
| Matteo Lancioni Ltd | Health & social care | 2024 |
| Matteucci Surgical Limited | Health & social care | 2019 |
| Matthew Zielonka Limited | Real estate | 2020 |
| Matthias&Eric Limited | Transport & logistics | 2023 |
| Matts MOT Automotive Centre Ltd | Wholesale & retail | 2025 |
| Maty SI ANY Trans Ltd | Transport & logistics | 2023 |
| Maty&Isa Limited | Transport & logistics | 2023 |
| Maverick Assets Ltd | Real estate | 2020 |
| Maxfield Consultancy Services Ltd | Professional & scientific | 2025 |
| Maximum Solutions Ltd | Professional & scientific | 2025 |
| Maxwell Plumbing & Heating Limited | Other services | 2010 |
| Maya Logistic Eldi Ltd | Transport & logistics | 2026 |
| Mayfair Aviation Limited | Other services | 2011 |
| Mayfair-Tudor Limited | Hospitality | 2013 |
| Mayrenia Ltd | Information & communication | 2016 |
| MAZAK84 Ltd | Transport & logistics | 2017 |
| Mazex Ltd | Wholesale & retail | 2023 |
| Mazmotors 1 Ltd | Wholesale & retail | 2024 |
| MB Automotive Repairs Ltd | Wholesale & retail | 2025 |
| MB Maintenance Ltd | Construction | 2023 |
| MB Network Installations Limited | Information & communication | 2022 |
| MB Pubs Limited | Administrative & support | 2017 |
| MB Scunthorpe Ltd | Hospitality | 2026 |
| Mcarthur Agriculture (Holdings) Limited | Financial services | 2025 |
| Mcarthur Agriculture (T/A Mcarthur BDC) Ltd | Manufacturing | 1999 |
| Mcculloch & Parsons Limited | Financial services | 2021 |
| MCF Logistics Ltd | Transport & logistics | 2025 |
| MCG Freight Ltd | Transport & logistics | 2025 |
| Mcgregor Logistics (Cardiff) Limited | Transport & logistics | 2020 |
| Mcgregor Logistics (Doncaster) Limited | Transport & logistics | 2008 |
| Mcgregor Logistics (South Wales) Limited | Transport & logistics | 2017 |
| Mcgregor Logistics (Warehousing) Limited | Transport & logistics | 2021 |
| Mchale Construction & Civils Ltd | Construction | 2025 |
| Mckinnon Mortgages Limited | Financial services | 2024 |
| MCP Trans Ltd | Transport & logistics | 2025 |
| Mctyres Scunthorpe Ltd | Wholesale & retail | 2026 |
| MD Aesthetics Ltd | Health & social care | 2015 |
| MD Holmes Decorating Services Ltd | Construction | 2023 |
| MDD New Trans Ltd | Transport & logistics | 2025 |
| MDH Homes Ltd | Real estate | 2026 |
| Mdhorizon Ltd | Wholesale & retail | 2026 |
| MDL Shipping Limited | Transport & logistics | 2011 |
| MEA Services Ltd | Health & social care | 2024 |
| Meat & Bread Catering Ltd | Hospitality | 2024 |
| Medallion Restaurant Ltd | Hospitality | 2024 |
| Medenco Limited | Health & social care | 2003 |
| Medesurg UK Ltd | Health & social care | 2022 |
| Medfiz Limited | Health & social care | 2021 |
| Medi Wise Care Ltd | Health & social care | 2024 |
| Medianimation Limited | Health & social care | 2021 |
| Medical and Fire Services Ltd | Professional & scientific | 2020 |
| Medical Skillsuk Ltd | Health & social care | 2012 |
| Medigeeks Consultancy Ltd | Professional & scientific | 2020 |
| Medl Properties Ltd | Real estate | 2026 |
| Medniq Services Ltd | Health & social care | 2025 |
| Medtrans Ltd | Transport & logistics | 2025 |
| Mega Electrical Services Ltd | Construction | 2024 |
| Megna Curry Company (Scunthorpe) Limited | Hospitality | 2010 |
| Mehmoods Property Investments Ltd | Real estate | 2025 |
| Meja Ltd | Transport & logistics | 2014 |
| Mejers Pharmacy Ltd | Wholesale & retail | 2023 |
| Mel's Totstop Limited | Education | 2010 |
| Melay Ltd | Health & social care | 2025 |
| Memo GAS Limited | Health & social care | 2019 |
| Menthand Physiotherapy and Wellness Clinic Ltd | Wholesale & retail | 2026 |
| Mercury First AID Ltd | Wholesale & retail | 2022 |
| Mercury Houses Ltd | Real estate | 2023 |
| Merge Technology Services Ltd | Construction | 2019 |
| Merge Traffic Management Ltd | Construction | 2019 |
| Meridian Materials Supply Limited | Financial services | 2003 |
| Merle Clothing Ltd | Wholesale & retail | 2024 |
| Messingham Car Care Limited | Wholesale & retail | 2003 |
| Messingham Equestrian and Livery Limited | Arts & recreation | 2021 |
| Messingham Flats Management Company Ltd | Households | 2008 |
| Messingham Freight Transport Ltd | Professional & scientific | 2018 |
| Messingham Golfing Supplies Limited | Wholesale & retail | 2026 |
| Messingham Martial Arts Ltd | Education | 2023 |
| Messingham Packaging Limited | Administrative & support | 2024 |
| Messingham Sands Fishery Ltd | Agriculture & fishing | 2020 |
| Messingham Storage Limited | Other services | 2024 |
| Messingham ZOO Ltd | Arts & recreation | 2018 |
| Metanoia Training and Consultancy Ltd | Other services | 2023 |
| Metcom Services Ltd | Construction | 2024 |
| MFI Properties (Lincs) Limited | Real estate | 2025 |
| MFM Developments Limited | Real estate | 2000 |
| MFO Construction Ltd | Construction | 2023 |
| MFP Acquisition Holding Limited | Professional & scientific | 2019 |