| Milloteck Ltd | Manufacturing | 2025 |
| Millson Hospitality Ltd | Hospitality | 2022 |
| Millstone Property Group Ltd | Construction | 2026 |
| Milmar Ltd | Real estate | 2020 |
| Milo Development BA Limited | Construction | 2018 |
| Milton Keynes Forklift Limited | Administrative & support | 2001 |
| Mind Matters Therapy Ltd | Health & social care | 2019 |
| Mind Science Ltd | Professional & scientific | 2019 |
| Mindclarity Clinical Services Ltd | Professional & scientific | 2026 |
| Mindful Beginnings Ltd | Health & social care | 2021 |
| Mini Major Club Limited | Information & communication | 2026 |
| Mini ME and MOM Ltd | Other services | 2021 |
| Mini Minds Childcare Ltd | Health & social care | 2019 |
| Mini Mover Removals Limited | Other services | 2023 |
| Miran 2024 Ltd | Hospitality | 2024 |
| Miranda Menzies Property Expert Limited | Real estate | 2022 |
| Mish Ltd | Construction | 2019 |
| Miss Cavalier Ltd | Agriculture & fishing | 2026 |
| Missk Events Ltd | Hospitality | 2021 |
| Mister Miller Limited | Manufacturing | 2020 |
| Mistik Ltd | Hospitality | 2019 |
| Mititelu Car Repairs Ltd | Wholesale & retail | 2017 |
| Mizzy Pet Store Ltd | Manufacturing | 2020 |
| Mizzy RAW Ltd | Wholesale & retail | 2026 |
| MJ Atkins Property Ltd | Construction | 2021 |
| MJ Customer Management Limited | Professional & scientific | 2008 |
| MJ Solutions Midlands LLP | | 2025 |
| MJB Consulting Engineers Ltd | Construction | 2025 |
| MJC Smart Repairs Ltd | Wholesale & retail | 2023 |
| MJF Moss Engineering Limited | Professional & scientific | 2026 |
| MJO Performance Ltd | Wholesale & retail | 2017 |
| Mjrh Holdings Ltd | Financial services | 2018 |
| MK Battery International Limited | Wholesale & retail | 2001 |
| MK Meded Services Ltd | Education | 2026 |
| MK Move Ltd | Other services | 2026 |
| Mk&Ln Ltd | Transport & logistics | 2015 |
| MKD Cargo Limited | Transport & logistics | 2023 |
| Mkfl Holdings Limited | Professional & scientific | 2008 |
| MKN Transport Ltd | Transport & logistics | 2018 |
| ML (Heysham) Limited | Construction | 2014 |
| ML Property Renovations and Maintenance Ltd | Construction | 2019 |
| Mlam Property Limited | Real estate | 2023 |
| MLM Plata Limited | Wholesale & retail | 2018 |
| MLS Air Conditioning Installations Limited | Construction | 2020 |
| MLS Air Conditioning Services Limited | Administrative & support | 2017 |
| MM Energy Services Ltd | Construction | 2025 |
| MMS Foodstuffs Limited | Wholesale & retail | 2025 |
| MMV Contracting Limited | Construction | 2004 |
| MN Clothing Ltd | Water & waste | 2015 |
| MN Construction Line Limited | Construction | 2023 |
| MO Latif ENT Limited | Health & social care | 2022 |
| Mobility Your Way Ltd | Wholesale & retail | 2018 |
| Mobius Homes Limited | Construction | 2026 |
| Mobius Services Limited | Professional & scientific | 2006 |
| Mobius Ventures Limited | Real estate | 2015 |
| Modern-Expo UK Limited | Manufacturing | 2015 |
| Modesty Healthcare Ltd | Health & social care | 2021 |
| MOG Brick Limited | Construction | 2020 |
| Mohfat Care Ltd | Health & social care | 2023 |
| Mojo Pinball Limited | Manufacturing | 2023 |
| Moksha Monkey Ltd | Financial services | 2021 |
| Mole Solutions Limited | Transport & logistics | 2002 |
| Molni Ltd | Wholesale & retail | 2020 |
| Momentera Limited | Professional & scientific | 2013 |
| MON Cuina Bistros Ltd | Hospitality | 2025 |
| Monkey Tree Hosting Ltd | Information & communication | 2012 |
| Monse Prime Limited | Construction | 2025 |
| Montagu OFF Licence Limited | Wholesale & retail | 2023 |
| Montgomery Refurbishments Limited | Construction | 2018 |
| Moon HSP Ltd | Transport & logistics | 2023 |
| Moon LEE Limited | Wholesale & retail | 2019 |
| Moore's Management Services Ltd | Professional & scientific | 2025 |
| Moorgate House (2017) Limited | Real estate | 2017 |
| More Construction Ltd | Construction | 2021 |
| More Fire PR Ltd | Professional & scientific | 2015 |
| Morfords Limited | Hospitality | 2025 |
| Morganwhite Ltd | Administrative & support | 2010 |
| Morris & Bert Water Solutions Ltd | Construction | 2020 |
| Morris Healthcare Group Limited | Health & social care | 2024 |
| Morris INK Limited | Other services | 2025 |
| Mortar & Co Construction Management Limited | Professional & scientific | 2018 |
| Mortar & Co Special Projects Limited | Construction | 2018 |
| MOT Consultant U.K. Limited | Education | 2026 |
| Motary Limited | Wholesale & retail | 2025 |
| Motion Motor Group Ltd | Wholesale & retail | 2022 |
| Motion Retail Solutions Limited | Construction | 2018 |
| Moto DUO Limited | Wholesale & retail | 2015 |
| Motogear Holdings Ltd | Professional & scientific | 2005 |
| Motogear Limited | Administrative & support | 2000 |
| Motor Monster Garage Ltd | Wholesale & retail | 2025 |
| Motor Monster Limited | Wholesale & retail | 2022 |
| Motorcross Limited | Administrative & support | 1985 |
| Moulton Leys Electrical Limited | Construction | 2005 |
| Mount Joyce Care Ltd | Health & social care | 2021 |
| Mount My Medals Ltd | Wholesale & retail | 2021 |
| Movenetwork Ltd | Transport & logistics | 2025 |
| Mowbotics UK Limited | Administrative & support | 2026 |
| Mown & Grown Landscaping Ltd | Administrative & support | 2020 |
| Moxjo Ltd | Manufacturing | 2025 |
| Moxy Textiles Limited | Wholesale & retail | 2026 |