| Metset Ltd | Other services | 2017 |
| Mexybrown Global Services Ltd | Health & social care | 2023 |
| Mfnh Limited | Education | 2025 |
| MG Mechanical Ltd | Construction | 2020 |
| MG Medsec Ltd | Administrative & support | 2022 |
| MI Salon Limited | Financial services | 2025 |
| Micdrop Digital Productions Limited | Professional & scientific | 2020 |
| Michael Miller & Partners Limited | Other services | 2001 |
| Michelle Osman Limited | Financial services | 2017 |
| MID Hants Ltd | Transport & logistics | 2012 |
| MID Hants Mowers Limited | Manufacturing | 2014 |
| MID Hants Storage Limited | Administrative & support | 2001 |
| Midas Tours Limited | Administrative & support | 2006 |
| Midwinter Post Limited | Other services | 2018 |
| Mifel Ltd | Financial services | 2025 |
| Mikado Equine Ltd | Wholesale & retail | 2012 |
| Milarepa Productions Ltd | Information & communication | 2024 |
| Mill House Coffee Ltd | Hospitality | 2024 |
| Milton James Limited | Other services | 1996 |
| Milton Keynes (T) Hairdressing Limited | Other services | 2006 |
| Mimikin Ltd | Professional & scientific | 2022 |
| Mimosa Retail Limited | Wholesale & retail | 2005 |
| Mindful Acoustics Limited | Information & communication | 2025 |
| Mindful Classics and Sportscars Limited | Extraterritorial | 2012 |
| Minerva Commodities Limited | Financial services | 2010 |
| Minerva Global Limited | Administrative & support | 2015 |
| Minerva House Export Finance Company Limited | Financial services | 2016 |
| Mint Condition (UK) Ltd | Arts & recreation | 1999 |
| Misat Limited | Information & communication | 2022 |
| MJ Wells Garden Services Limited | Other services | 2002 |
| MJG 1968 Consulting Limited | Other services | 2022 |
| MJK Spice Ltd | Hospitality | 2026 |
| Mjsd Consulting Limited | Professional & scientific | 2013 |
| MK Food Services Ltd | Hospitality | 2020 |
| MKD Property Maintenance Ltd | Construction | 2025 |
| MMM2CK Trading AS Corporate Occupational Health Ltd | Health & social care | 2025 |
| Mobile Incar Ltd | Wholesale & retail | 2013 |
| Model Farm Storage Limited | Real estate | 2022 |
| Modellbauuk Limited | Wholesale & retail | 2012 |
| Modern Twist LAB Ltd | Wholesale & retail | 2018 |
| Momma Bird Ltd | Arts & recreation | 2023 |
| Monkey Lord Limited | Wholesale & retail | 2014 |
| Moorley Property Lettings LLP | | 2024 |
| Morbean Communications Ltd | Professional & scientific | 2013 |
| MORE4X4 Restorations Limited | Transport & logistics | 2022 |
| Moss Consulting and Advisory Ltd | Professional & scientific | 2016 |
| Motion Workbooks Ltd | Information & communication | 2025 |
| Motoline Limited | Wholesale & retail | 2019 |
| Mott 32 (London) Ltd. | Hospitality | 2024 |
| Mouflon Solutions Limited | Professional & scientific | 2015 |
| Moulsford Limited | Construction | 1997 |
| Mountain Logistic Operations Limited | Transport & logistics | 2018 |
| Mountain Print Limited | Manufacturing | 2021 |
| Movenext Property Management Company Limited | Households | 1998 |
| Moviehouse Entertainment Limited | Information & communication | 2001 |
| Moving Doormats Limited | Real estate | 2020 |
| MOW N Blow Designs Limited | Professional & scientific | 2017 |
| Mowmacre Investment and Charter Limited | Real estate | 1934 |
| Moyle Corporation Co. | Financial services | 2025 |
| Moyralla Marketing Limited | Administrative & support | 2023 |
| MOZ Property Ltd | Real estate | 2024 |
| MP Logistics Network Ltd | Transport & logistics | 2026 |
| MPO Consulting Limited | Professional & scientific | 2004 |
| MPS Plumbing Solutions Limited | Construction | 2006 |
| MR Repairs Ltd | Other services | 2018 |
| MR. Whitehead's Cider Company Ltd | Manufacturing | 2003 |
| MR. Whitehead's Drinks Company Ltd. | Manufacturing | 2012 |
| MS@@ Limited | Wholesale & retail | 2024 |
| MSY Protect Limited | Administrative & support | 2023 |
| MTG Consultancy Services Ltd | Professional & scientific | 2023 |
| MTN Holdings Limited | Financial services | 2023 |
| MTS 4X4 Ltd | Wholesale & retail | 2013 |
| Mullard Funerals Ltd | Other services | 1997 |
| Multi Marine Offshore Services Ltd | Transport & logistics | 2011 |
| Multidisciplinary Health and Wellbeing Team Online Limited | Public administration | 2022 |
| Murrell Brothers Ltd | Construction | 2022 |
| Musculoskeletal Imaging Limited | Health & social care | 2011 |
| Muzaiq Ltd | Information & communication | 2025 |
| MVV Rentals (1) Phuket Ltd | Hospitality | 2015 |
| MVV Rentals (2) Phuket Ltd | Hospitality | 2015 |
| My Beauty Salon Limited | Other services | 2010 |
| My Hair and Beauty Salon Limited | Other services | 2015 |
| My Photo Furnishings Ltd | Manufacturing | 2019 |
| My Streats Ltd | Information & communication | 2022 |
| My Sunny Ltd | Wholesale & retail | 2013 |
| Mycroft Homes Limited | Real estate | 2002 |
| Myice Guardian Limited | Wholesale & retail | 2025 |
| N B Heating & Plumbing Services Ltd | Construction | 2016 |
| N S Building Contractors Limited | Construction | 2016 |
| N&C Slorach Ltd | Other services | 2017 |
| N.James Slorach Limited | Financial services | 2015 |
| NAC Engineers Ltd | Professional & scientific | 2014 |
| Narrum Limited | Financial services | 2026 |
| Naturetrek Limited | Administrative & support | 1997 |
| Nebula Energy Ltd | Construction | 2021 |
| Neilsed Limited | Information & communication | 2013 |
| Nell Properties Ltd | Real estate | 2021 |
| Netconsent Ltd | Information & communication | 2004 |
| Netrin Ltd | Manufacturing | 2020 |
| Netsus Ltd | Professional & scientific | 1995 |