| MD1 Clearance Ltd | Water & waste | 2023 |
| MD1 Removals Ltd | Transport & logistics | 2021 |
| MDG Audits Limited | Construction | 2025 |
| Meadows Honey Limited | Manufacturing | 2020 |
| Mechanical Services UK Ltd | Manufacturing | 2005 |
| Mega Grill Pizza Limited | Hospitality | 2026 |
| Melhor Care Ltd | Health & social care | 2021 |
| Melton Mowbray 3 Limited | Other services | 2022 |
| Membranetec Ltd | Construction | 2025 |
| Mera - the Green Connect Limited | Administrative & support | 2023 |
| Meridium Labs Ltd | Professional & scientific | 2026 |
| Merriefield Farms Limited | Agriculture & fishing | 1978 |
| Meter MIX Systems Limited | Manufacturing | 1989 |
| Metters Security Limited | Administrative & support | 2017 |
| Mezin Ltd | Hospitality | 2026 |
| MF Constructions (U.K) Ltd | Construction | 2023 |
| MG & C Services Limited | Construction | 2014 |
| MIA MAE Bridal House Ltd | Other services | 2022 |
| Mick Allen & SON Aircraft Resprays Limited | Manufacturing | 2012 |
| Micromat Limited | Information & communication | 2021 |
| Midas Strategies (UK) LLP | | 2005 |
| Midas Strategies Limited | Extraterritorial | 2005 |
| Midland Automation Limited | Manufacturing | 1971 |
| Midland Counties Fencing Ltd | Construction | 2020 |
| Midlands Compost Ltd | Wholesale & retail | 2022 |
| Midon Services Limited | Other services | 2017 |
| Milliemm Ltd | Wholesale & retail | 2024 |
| Milton Keynes Arts Centre Ltd | Arts & recreation | 1991 |
| Milton Keynes London Link Limited | Transport & logistics | 1991 |
| Miltonbury Installations Limited | Construction | 2022 |
| Ministry of ME Limited | Administrative & support | 2013 |
| Mint GB Stamps Limited | Wholesale & retail | 2013 |
| Mirum Potis Logitics Ltd | Transport & logistics | 2024 |
| Misco Technologies Limited | Information & communication | 2009 |
| Mistrys Developments Limited | Construction | 2020 |
| Mistrys Group Ltd | Financial services | 2015 |
| Mistrys Healthy Options Limited | Wholesale & retail | 1988 |
| Mitsui Seiki USA (UK) Limited | Manufacturing | 2012 |
| Mixco Limited | Manufacturing | 1997 |
| MJ Event Contracting Ltd | Administrative & support | 2025 |
| Mjht Ltd | Information & communication | 2023 |
| MJJ Investments Co. Limited | Wholesale & retail | 2010 |
| MJM Property Management Limited | Real estate | 2005 |
| MK Sports Management Ltd | Arts & recreation | 2022 |
| Mkel Limited | Health & social care | 2014 |
| ML981 Limited | Hospitality | 2018 |
| Mmcité UK Ltd | Wholesale & retail | 2016 |
| Mmevolution Ltd | Education | 2015 |
| MN13 Carpentry Ltd | Construction | 2025 |
| Mnhakwi Care Ltd | Health & social care | 2014 |
| MO Money Financial Services Ltd | Financial services | 2019 |
| Mobiledoc Gadgets Repair Centre Ltd | Wholesale & retail | 2020 |
| Mobiles and More Limited | Information & communication | 2024 |
| Mocca Mocca Ltd | Professional & scientific | 2009 |
| Modernaire Business Solutions Ltd | Professional & scientific | 2015 |
| Mongoose and Swan Limited | Professional & scientific | 2011 |
| Monoworld Group PLC | Water & waste | 2012 |
| Monoworld Limited | Water & waste | 2000 |
| Monoworld Recycling Ltd | Water & waste | 2007 |
| Moore Hopkins Limited | Professional & scientific | 2016 |
| Moose Maintenance Limited | Households | 2024 |
| Morado Holdings Ltd | Financial services | 2023 |
| Mordon Properties Limited | Real estate | 2018 |
| Morgan Group Holdings Limited | Real estate | 2017 |
| Morson & Co Associates Ltd | Professional & scientific | 2017 |
| Morton Consultancy Services Ltd | Information & communication | 2022 |
| Moss Court RTM Company Limited | Real estate | 2012 |
| Motormeld Ltd | Manufacturing | 2025 |
| MP Distribution Services Limited | Construction | 2022 |
| MR Elixir Ltd | Transport & logistics | 2021 |
| MRC Holdings Limited | Other services | 2019 |
| MS Consulting Global Limited | Administrative & support | 2015 |
| MTD Ebusiness Ltd | Professional & scientific | 2009 |
| MTD Health Limited | Manufacturing | 2026 |
| Mtre Group Ltd | Financial services | 2020 |
| Mtre Limited | Real estate | 2018 |
| Mukai Ltd | Professional & scientific | 2018 |
| Multiassistance Ltd | Administrative & support | 2016 |
| Munns Kerb Layers Ltd | Construction | 2019 |
| Mutual Homes Limited | Real estate | 2002 |
| Muzondo Health Limited | Health & social care | 2018 |
| MW Flooring & Interiors Limited | Construction | 2023 |
| MW Post Ltd | Transport & logistics | 2026 |
| MX Showertrays Limited | Extraterritorial | 1991 |
| My Family Mortgages Ltd | Financial services | 2019 |
| Myle Logistics Ltd | Transport & logistics | 2018 |
| N & P Clinic Ltd | Health & social care | 2025 |
| N T Cooling Services Limited | Construction | 2019 |
| N W K R Limited | Administrative & support | 2015 |
| N&N Automation Ltd | Information & communication | 2014 |
| N. Stephens & Co. Ltd | Professional & scientific | 2000 |
| N2 Trades Limited | Information & communication | 2024 |
| Nail IT N' Grow Limited | Construction | 2025 |
| Nail Plus GP Ltd | Other services | 2025 |
| Nailed IT Property Services Limited | Water & waste | 2021 |
| Naja Holdings Limited | Wholesale & retail | 2024 |
| Naja Investments Limited | Wholesale & retail | 2019 |
| Nanno Consulting Ltd | Professional & scientific | 2025 |
| Nathan Godby Limited | Other services | 2022 |
| Nats and Bolts Ltd | Extraterritorial | 2021 |