| M Toporek Driving Services Ltd | Transport & logistics | 2011 |
| M Wheatley Plumbing and Heating Ltd | Construction | 2018 |
| M Wilson Projects Ltd | Construction | 2022 |
| M&A Spedition Ltd | Transport & logistics | 2023 |
| M&G Plumbing and Heating Ltd | Construction | 2024 |
| M&H Afro and European Beauty Hair Studio Ltd | Other services | 2024 |
| M&H Builders Limited | Construction | 2016 |
| M&M Staffing Limited | Transport & logistics | 2014 |
| M. Donovan Heating Limited | Construction | 2021 |
| M. Hannon Limited | Construction | 1975 |
| M. S. Legal Services Limited | Professional & scientific | 2002 |
| M. Smith & SON ( Fruiterers ) Ltd | Hospitality | 2014 |
| M.A. Simmonds Installations Limited | Construction | 2005 |
| M.A.M. Carpentry Ltd | Manufacturing | 2026 |
| M.Ch. Auto Repair Ltd | Wholesale & retail | 2023 |
| M.E.L. Hospitality Ltd | Hospitality | 2024 |
| M.G.M Care Response Limited | Health & social care | 2021 |
| M.R.M. Graphics Limited | Administrative & support | 1973 |
| M.S Roberts Landscaping Ltd | Administrative & support | 2016 |
| M3DIA-PRO Ltd | Information & communication | 2015 |
| M3X Ltd | Information & communication | 2019 |
| Maab Consulting Limited | Professional & scientific | 2024 |
| Maarua Management Limited | Professional & scientific | 2026 |
| Maassist Limited | Other services | 1996 |
| Maaze Ltd | Health & social care | 2022 |
| Mabels House Ltd | Professional & scientific | 2022 |
| Mabey Properties Ltd | Real estate | 2011 |
| Maccers Constructions Ltd | Professional & scientific | 2024 |
| Mach One Engineering Limited | Manufacturing | 2009 |
| Machine Engineering Ltd | Manufacturing | 2026 |
| Machine Garage Limited | Professional & scientific | 2022 |
| Machpro Solutions Limited | Professional & scientific | 2026 |
| Mack Distribution Ltd | Wholesale & retail | 2020 |
| Macksy Prints Ltd | Manufacturing | 2023 |
| Madappattu Ltd | Health & social care | 2015 |
| Madhavrama Limited | Real estate | 2025 |
| Madz Wholesale Ltd | Wholesale & retail | 2025 |
| MAF Residence Ltd | Construction | 2023 |
| MAG Advisory Limited | Professional & scientific | 2020 |
| MAG Home Claims Services Limited | Other services | 2020 |
| MAG JAZ Ltd | Information & communication | 2019 |
| Magenta Homes (UK) Limited | Wholesale & retail | 2005 |
| Maggie Parker Consultancy Ltd | Professional & scientific | 2026 |
| Magic EYE Cleaning Ltd | Administrative & support | 2026 |
| Magic Groundworks Ltd | Construction | 2025 |
| Magic Hues Limited | Information & communication | 2016 |
| Magic Marius Ltd | Arts & recreation | 2024 |
| Magic-Wand.Com Limited | Professional & scientific | 2005 |
| Magicman Holdings Limited | Manufacturing | 2018 |
| Magna Thorpe Ltd | Professional & scientific | 2002 |
| Magnetar Access Limited | Professional & scientific | 2023 |
| Magnetic Resolutions Limited | Professional & scientific | 2021 |
| Magnolia Assets Limited | Construction | 2022 |
| Magpies Inn Limited | Hospitality | 2014 |
| Magrathea Technology Ltd | Manufacturing | 2020 |
| Magroup Limited | Professional & scientific | 2008 |
| Mags Services Limited | Information & communication | 2019 |
| Maha Trading PVT Ltd | Wholesale & retail | 2024 |
| Maiar Investments Limited | Real estate | 2020 |
| Maisie Elizabeth Cosmetics Ltd | Other services | 2020 |
| Maiya Property Group Ltd | Financial services | 2025 |
| Maizk Limited | Information & communication | 2019 |
| Majdan Property Limited | Real estate | 2025 |
| Majestic Developments Ltd | Construction | 2024 |
| Major Collectables Ltd | Wholesale & retail | 2026 |
| Major Transformational Coaching Ltd | Education | 2023 |
| Maka Sales Ltd | Wholesale & retail | 2022 |
| Makeadish Ltd | Information & communication | 2026 |
| Making Business Matter Limited | Professional & scientific | 2006 |
| Makris Medical Ltd | Health & social care | 2021 |
| Maksel Services Ltd | Construction | 2026 |
| Maksons Convenience Retail Ltd | Wholesale & retail | 2022 |
| Maksons Fuels Retail Ltd | Wholesale & retail | 2024 |
| Malabar Consulting Limited | Professional & scientific | 2004 |
| Malk Holdings Ltd | Financial services | 2025 |
| Malleya Ltd | Information & communication | 2020 |
| Malt and Grapes Ltd | Wholesale & retail | 2024 |
| Maluki and Holmes Asset Management Limited | Real estate | 2024 |
| Mam's Online Digital Business Ltd | Professional & scientific | 2025 |
| Mammoth Air- Conditioning and Refrigeration Ltd | Professional & scientific | 2019 |
| Mammoth Entertainment Ltd | Arts & recreation | 2026 |
| Mammoth Services Ltd | Construction | 2015 |
| MAN LEE Property Ltd | Real estate | 2020 |
| Manang Momo Limited | Hospitality | 2021 |
| Mancasso Ltd | Wholesale & retail | 2023 |
| Mandate Healthcare Ltd | Public administration | 2022 |
| Mandeville Cash & Carry Ltd | Wholesale & retail | 2024 |
| Mandeville Medicines Limited | Manufacturing | 2001 |
| Manfi Property Ltd | Real estate | 2018 |
| Manhattan INK Aylesbury Ltd | Arts & recreation | 2018 |
| Manhole Covers Limited | Wholesale & retail | 1992 |
| Manifest Partnerships Ltd | Professional & scientific | 2026 |
| Manju Health Services Limited | Health & social care | 2023 |
| Manlet Estates Limited | Professional & scientific | 1973 |
| Manning White Limited | Real estate | 2018 |
| Mano Media Ltd | Information & communication | 2024 |
| Manor Contracts (UK) Limited | Other services | 2002 |
| Manor Court (Highgate) Management Limited | Households | 1997 |
| Manor Farm Biodiversity Limited | Agriculture & fishing | 2024 |
| Manor Farm Dixton Ltd | Hospitality | 2025 |