| M-Tech Bodyshop Limited | Wholesale & retail | 2007 |
| M-Tech South East Ltd | Wholesale & retail | 2025 |
| Madabout Magnets Ltd | Wholesale & retail | 2025 |
| Maerose Distillery Ltd | Manufacturing | 2021 |
| Mahouse Ltd | Hospitality | 2024 |
| Maisville Properties Ltd | Real estate | 2022 |
| Maisville Property Group Ltd | Real estate | 2024 |
| Majikku Limited | Arts & recreation | 2010 |
| Maker Property Investing Ltd | Real estate | 2025 |
| Maker&Son Holdings Ltd | Financial services | 2021 |
| Makin PR Limited | Professional & scientific | 2007 |
| Makita's Tutoring Ltd | Professional & scientific | 2023 |
| Mamaligar Software Ltd | Information & communication | 2023 |
| Mane Painting Co Ltd | Construction | 2026 |
| Mangales Ltd | Wholesale & retail | 2020 |
| Markov Enterprise Ltd | Wholesale & retail | 2024 |
| Marpe Kalos Ltd | Health & social care | 2020 |
| Martial Arts Studies Association CIC | Other services | 2025 |
| Martirossian Training Academy Ltd | Education | 2018 |
| Massala Express Seaford Ltd | Hospitality | 2023 |
| Matt Anderson Ltd | Professional & scientific | 2006 |
| Matt Mitchell Heritage & Traditional Screeding Limited | Construction | 2017 |
| Matthias Ossyra Ltd | Professional & scientific | 2013 |
| MAY Connections Ltd | Construction | 2020 |
| Mayfield Osteopaths Limited | Health & social care | 2014 |
| Maypole Grants Ltd | Other services | 2023 |
| Mays Farm Limited | Agriculture & fishing | 1995 |
| Mbcommerce Limited | Information & communication | 2000 |
| MC Maxx Limited | Wholesale & retail | 2015 |
| Mccann Rail Ltd | Construction | 2015 |
| Mccloy Marketing Services Ltd | Professional & scientific | 2023 |
| Mcguires Wires Electrical Ltd | Construction | 2023 |
| MCL Star Group Ltd | Construction | 2024 |
| Mclub Leadership Development & Executive Coaching Ltd | Other services | 2015 |
| MD Resource Limited | Professional & scientific | 2010 |
| MD Staffs Energy Collection Ltd | Other services | 2016 |
| MDJ Services Limited | Professional & scientific | 1997 |
| Meadows Cafe & Store Ltd | Wholesale & retail | 2019 |
| Meaningful Futures CIC | Professional & scientific | 2025 |
| Mechalab Ltd | Information & communication | 2011 |
| Media Bite Ltd | Professional & scientific | 2024 |
| Media Distribution Agency Ltd | Information & communication | 2015 |
| Media Sales Group Ltd | Professional & scientific | 2018 |
| Meeching Ceramic Tiling Ltd | Construction | 2016 |
| MEG Taylor OBC Limited | Transport & logistics | 2024 |
| Meggs Management Ltd | Professional & scientific | 2013 |
| Melted Inside International Ltd | Wholesale & retail | 2019 |
| Memzi Ltd | Extraterritorial | 2018 |
| Mental Health Coaching Ltd | Health & social care | 2020 |
| Merchant Turnaround PLC | Financial services | 2010 |
| Merlin Tuition Limited | Administrative & support | 2020 |
| Metis Ventures Ltd | Professional & scientific | 2025 |
| Metrix Contractors Limited | Construction | 2014 |
| Metropole Court (Eastbourne) Limited | Households | 1985 |
| Metsuki Ltd | Construction | 2013 |
| MF Fire Door Inspections Ltd | Construction | 2019 |
| Mgcs Automotive Ltd | Wholesale & retail | 2023 |
| MHB Aviation Consultants Limited | Professional & scientific | 2004 |
| Michael Madden Consulting Limited | Professional & scientific | 2021 |
| Micro Camper Accessories Ltd | Manufacturing | 2023 |
| Middleton Heating and Plumbing Limited | Construction | 2009 |
| Midgard Marketing Ltd | Information & communication | 2018 |
| Mighty Builders Construction Ltd | Construction | 2025 |
| Milkfloat Projections CIC | Other services | 2020 |
| Millar & Co (Sussex) Ltd | Real estate | 2012 |
| Millars Classic and Sports Ltd | Extraterritorial | 2013 |
| Millennial Homes England Limited | Real estate | 2019 |
| Minali Ltd | Professional & scientific | 2014 |
| Mitchell Private Clients Limited | Financial services | 2019 |
| Mitchell Property Investments Limited | Real estate | 2015 |
| MJL Carpentry Limited | Construction | 2014 |
| MJR Markets Ltd | Administrative & support | 2019 |
| MJT Legal Ltd | Professional & scientific | 2026 |
| ML Cleaning Services Ltd | Administrative & support | 2025 |
| ML4GOOD Ltd | Education | 2024 |
| Moat House Flats Limited | Households | 1957 |
| Mobile Compactor Services Limited | Water & waste | 1998 |
| Moda Matinee Limited | Wholesale & retail | 2025 |
| Mogul Screen Limited | Information & communication | 2017 |
| Monkey Tree TV Ltd | Information & communication | 2004 |
| Monrovia Solutions Ltd | Wholesale & retail | 2006 |
| Morgan Nash Events Limited | Administrative & support | 2023 |
| Morley Electrical Services Limited | Construction | 2003 |
| Moseprop Ltd | Real estate | 2016 |
| Mossala Takeaway Limited | Hospitality | 2019 |
| Mostami Limited | Wholesale & retail | 2020 |
| Moto Teardown Ltd | Wholesale & retail | 2022 |
| Mountfield House (Lewes) Limited | Households | 2003 |
| MPD Executive Consultants Ltd | Administrative & support | 2022 |
| MPH Landscaping 2 Driveways Ltd | Professional & scientific | 2021 |
| MR Unicorn Ltd | Education | 2025 |
| Mrdek Ltd | Arts & recreation | 2018 |
| MS Roofing Supplies Limited | Wholesale & retail | 2006 |
| Mshk Ltd | Professional & scientific | 2014 |
| Msmatch Ltd | Wholesale & retail | 2014 |
| Mumma K'S Walkies Limited | Other services | 2025 |
| My Broker UK Ltd | Financial services | 2019 |
| My Notary Public Ltd | Professional & scientific | 2021 |
| My Salon Business Coach Ltd | Professional & scientific | 2018 |
| My Urban Tribe Limited | Information & communication | 2013 |