| Make IT Real Technologies Limited | Information & communication | 2023 |
| Maksimus Consultancy Services Ltd | Professional & scientific | 2022 |
| Maltby Property Portfolio Ltd | Real estate | 2025 |
| Manor Transport (Arundel) Ltd | Transport & logistics | 2003 |
| Many Happy Returns for Generations Limited | Administrative & support | 2006 |
| Many Oaks Consultancy Limited | Professional & scientific | 1995 |
| Maple Family Ltd | Other services | 2021 |
| Maplecharm Limited | Households | 1994 |
| Marge Holdings Limited | Financial services | 2023 |
| Mark Stevens Builders Limited | Extraterritorial | 2015 |
| Mark Stevens General Builder Ltd | Construction | 2013 |
| Mark Stevens Properties Limited | Real estate | 2020 |
| Marked Home Improvements Ltd | Construction | 2013 |
| Market Gardens Fairlight Management Limited | Households | 2024 |
| Marlie Farm Holiday Village Limited | Hospitality | 1989 |
| Martello Beach Limited | Hospitality | 2013 |
| Martial Arts Teachers Limited | Education | 2007 |
| Martin Riley Ltd | Other services | 2014 |
| Martlet Investments Ltd | Real estate | 2012 |
| Marula African Foods & Meats Ltd | Wholesale & retail | 2026 |
| Mason & LIU Limited | Professional & scientific | 2007 |
| Massonetto Trading Ltd | Wholesale & retail | 2021 |
| Masteffy Holdings LLP | | 2022 |
| Match Senior Care Ltd | Health & social care | 2016 |
| Matevi Service Group Ltd | Manufacturing | 2019 |
| Mattonia Ltd | Real estate | 2019 |
| Maud Doris Ltd | Wholesale & retail | 2008 |
| Maxwell Cross Limited | Real estate | 2015 |
| Mayfair West Property Ltd | Real estate | 2024 |
| Mayfield Way Management Company Limited | Other services | 2004 |
| Mazzariti Ltd | Information & communication | 2016 |
| MBT Recruits Ltd | Administrative & support | 2021 |
| MC Glass (East Sussex) Limited | Construction | 1999 |
| MCJ Express Ltd | Transport & logistics | 2025 |
| Mclean Health Fitness & Nutrition Ltd | Wholesale & retail | 2026 |
| MD Property World Limited | Real estate | 2017 |
| MDH Cleaning Services Ltd | Administrative & support | 2024 |
| MDT Essex Ltd | Real estate | 2020 |
| ME Change Management Ltd | Professional & scientific | 2009 |
| Mebt Holdings Ltd | Financial services | 2021 |
| Mech Z Ltd | Construction | 2024 |
| Med-Jf Healthcare Ltd | Health & social care | 2022 |
| Media 66 Limited | Information & communication | 2020 |
| Mediagear Limited | Extraterritorial | 2015 |
| Meggs Driving Limited | Transport & logistics | 2021 |
| Meggs Finance Limited | Professional & scientific | 2020 |
| Meliorys Kapital Limited | Construction | 2021 |
| Melisande Securities Limited | Construction | 2010 |
| Melissa White Design Ltd | Professional & scientific | 2024 |
| Melrose Stores Limited | Hospitality | 1964 |
| Meneer House RTM Company Limited | Households | 2021 |
| Mepham & Wood Holdings Limited | Financial services | 2025 |
| Mepham & Wood Limited | Manufacturing | 2014 |
| Mepham & Wood Properties Limited | Real estate | 2025 |
| Mercia Road Sweepers Limited | Administrative & support | 2026 |
| Mercurian Prodigy Solutions Ltd. | Administrative & support | 2022 |
| Meteor Distribution Limited | Wholesale & retail | 2003 |
| Metropolitan Contractors Limited | Construction | 2019 |
| MEV Spares Limited | Administrative & support | 2012 |
| MEY House Ltd | Hospitality | 2025 |
| MG Square Limited | Real estate | 2018 |
| MGM Innovations Limited | Professional & scientific | 2023 |
| MGS Brickwork & General Building Limited | Construction | 2024 |
| Miccare Limited | Health & social care | 2019 |
| Miles Coote Queer Arts Limited | Wholesale & retail | 2021 |
| Miles SMT Ltd | Health & social care | 2019 |
| Millfield Court Limited | Households | 1957 |
| Milman Burdett Ltd | Professional & scientific | 2011 |
| Milton Contract Services Ltd | Construction | 2007 |
| Minaun Property Limited | Real estate | 2025 |
| Mind Art Ltd | Professional & scientific | 2018 |
| Mines a Pinot Limited | Health & social care | 2011 |
| Minx Properties Ltd | Hospitality | 2023 |
| Misfit Group Ltd | Other services | 2025 |
| Misha Patel Locum Services Limited | Health & social care | 2018 |
| MJ Windows and Maintenance Limited | Construction | 2024 |
| MJD Surveying Limited | Professional & scientific | 2014 |
| Mjrb Arts Limited | Professional & scientific | 2019 |
| MKS Designs Limited | Construction | 2007 |
| ML Consulting Group Ltd | Professional & scientific | 2018 |
| Mokd Ltd | Real estate | 2019 |
| Momentum Digital Solutions Limited | Professional & scientific | 2025 |
| Mona Commercial Group Ltd | Wholesale & retail | 2026 |
| Monkeys on the Moon Media Ltd | Information & communication | 2012 |
| Mont PIX Ltd | Real estate | 2017 |
| Moonsushi Bexhill Ltd | Hospitality | 2020 |
| Moore's Commercial Vehicle Repairs Ltd | Wholesale & retail | 2009 |
| Morntide Construction Limited | Construction | 2017 |
| Morter Electrical Ltd | Construction | 2015 |
| Mount Farm Property Ltd | Real estate | 2022 |
| Mount Hire Ltd | Administrative & support | 2021 |
| Moxam Formwork & Reinforcement Limited | Construction | 2000 |
| MR He's Savoury Kitchen Ltd | Hospitality | 2017 |
| MR Locks Locksmith Limited | Administrative & support | 2024 |
| MRS Mcgoo Limited | Wholesale & retail | 2018 |
| Mrs.Monro Limited | Professional & scientific | 1948 |
| Munday Finishes Ltd | Construction | 2018 |
| My Life ME Ltd | Health & social care | 2021 |
| My Paloma Ltd | Arts & recreation | 2024 |
| Myspires Stallions Ltd | Agriculture & fishing | 2025 |