| Marcopolo Business Services Limited | Professional & scientific | 2005 |
| Maria Paviour Company Ltd | Manufacturing | 2013 |
| Marianne House Management Company Limited | Households | 2001 |
| Marie-Louise Schlemm Ltd | Professional & scientific | 2010 |
| Marina Dolci Limited | Extraterritorial | 2021 |
| Marina Tanning Lounge Ltd | Other services | 2023 |
| Marina Village (Eastbourne) Management Company Limited | Households | 2003 |
| Marine Fish & Chips (Eastbourne) Limited | Hospitality | 2019 |
| Marine Trimming Limited | Manufacturing | 2020 |
| Mariners Walk "B" (Eastbourne) Management Company Limited | Households | 1995 |
| Maritime and Offshore Media Limited | Administrative & support | 2014 |
| Marius Jurcan Ltd | Wholesale & retail | 2019 |
| Mark Bishop Ltd. | Construction | 1999 |
| Mark Fagan Associates Limited | Administrative & support | 2009 |
| Mark Law Registrars Limited | Extraterritorial | 1997 |
| Mark Ludwig Consulting Ltd | Professional & scientific | 2023 |
| Mark My System Ltd | Information & communication | 2026 |
| Mark Ratcliffe Moving Limited | Administrative & support | 2017 |
| Marketing AID Limited | Other services | 1971 |
| Marling Associates Limited | Professional & scientific | 1999 |
| Marlow Residents Management Company Ltd | Households | 2008 |
| Marra Merchandise Ltd | Wholesale & retail | 2023 |
| Marrutt Limited | Manufacturing | 1981 |
| Marschall United Ltd | Manufacturing | 2017 |
| Marsh Accounting Limited | Professional & scientific | 2021 |
| Marsh Assets Ltd | Financial services | 2012 |
| Marsh Medical Accounts Ltd | Extraterritorial | 2021 |
| Marsh Medical Ltd | Extraterritorial | 2021 |
| Marshall Logging, Equipment Limited | Extraterritorial | 2000 |
| Marshall Murray Ltd | Wholesale & retail | 2011 |
| Martcoug UK Ltd | Wholesale & retail | 2025 |
| Martello Eastbourne Limited | Hospitality | 2025 |
| Martha's Matchbox Ltd | Arts & recreation | 2025 |
| Martin Janky Building Services Ltd | Construction | 2018 |
| Martin Onshore Developments Limited | Real estate | 2024 |
| Martlet Design Ltd | Professional & scientific | 2025 |
| Martlet Mobility Services Ltd | Professional & scientific | 2019 |
| Martlet Productions Limited | Administrative & support | 2014 |
| Martlets IFA Ltd | Financial services | 2009 |
| Martlets Residents Association Limited (the) | Households | 1970 |
| Martyn Ward Consulting Ltd | Professional & scientific | 2025 |
| Marusya Properties Limited | Real estate | 2009 |
| Mary Film Limited | Information & communication | 2017 |
| Marymel Ltd | Health & social care | 2022 |
| Maspatel Ltd | Wholesale & retail | 2023 |
| Massonclan Garden Maintenance Ltd | Administrative & support | 2012 |
| Master Eight Ltd | Financial services | 2005 |
| Masterplan Ventures Ltd | Administrative & support | 2013 |
| Masters of Creativity Ltd | Administrative & support | 2016 |
| Matara Global Limited | Information & communication | 2025 |
| Matmedia Productions Limited | Information & communication | 2002 |
| Matshaka Weavers Limited | Health & social care | 2022 |
| Matt Auto Repairs Ltd | Wholesale & retail | 2009 |
| Matt Smith Plumbing and Heating Limited | Construction | 2002 |
| Matthew Cheney Management Ltd | Arts & recreation | 2019 |
| Mavi Move Ltd | Real estate | 2024 |
| Max-Wax Fleet Holdings Limited | Financial services | 2023 |
| Max-Wax Fleet Investments Ltd | Financial services | 2023 |
| Max-Wax Fleet Ltd | Wholesale & retail | 2011 |
| Maxdata Limited | Administrative & support | 2008 |
| Maxden Limited | Construction | 2017 |
| Maxes (UK) Limited | Professional & scientific | 2024 |
| Maxus Limited | Information & communication | 2000 |
| Maya Cacao Ltd | Manufacturing | 2025 |
| Maybe Later Limited | Professional & scientific | 2024 |
| Maybury Woods Management Limited | Households | 2002 |
| Mayfair Bar Group Ltd | Hospitality | 2019 |
| Mayfair Jones Limited | Construction | 2019 |
| Mayfair Maintenance Ltd | Other services | 2010 |
| Maynard Holdings Limited | Real estate | 2021 |
| Mazesys Inc Ltd | Information & communication | 2013 |
| Mazika Digital Limited | Other services | 2020 |
| Mazoe Ltd | Health & social care | 2021 |
| MB Flow Limited | Professional & scientific | 2026 |
| Mbassett & Co Ltd | Information & communication | 2026 |
| MBC Vehicle Solutions Limited | Wholesale & retail | 2016 |
| MBH Wealth Management Limited | Financial services | 2009 |
| Mbouchiba Dental Limited | Health & social care | 2016 |
| MC Arry's Inns Ltd | Hospitality | 2015 |
| MC Style Limited | Wholesale & retail | 2024 |
| Mccarthy Webb Limited | Professional & scientific | 2009 |
| Mccreadie Meters Limited | Administrative & support | 2017 |
| Mcfagan Ltd | Agriculture & fishing | 2008 |
| Mcfagan Rentals Ltd | Real estate | 2024 |
| Mckay's Law Limited | Professional & scientific | 2023 |
| Mckenzie Associates Limited | Other services | 2014 |
| Mclsg Limited | Information & communication | 2025 |
| Mcmedia SW Ltd | Information & communication | 2012 |
| MCT Solicitors Ltd | Professional & scientific | 2021 |
| MD Media Ltd | Professional & scientific | 2025 |
| Mdecs (UK) Limited | Professional & scientific | 2009 |
| ME Hart Limited | Health & social care | 2024 |
| Meadow Way Business Park Ltd | Construction | 2019 |
| Meadowsweet Developments Limited | Administrative & support | 2014 |
| Meads Art & Design Limited | Professional & scientific | 2024 |
| Meads Court Residents Association (Eastbourne) Limited | Households | 1971 |
| Meads Dreams Limited | Health & social care | 2018 |
| Meads Gate Residents Association Limited | Households | 1961 |
| Meads Investment Group Ltd | Financial services | 2025 |
| Meads Lodge Residents Association Limited | Households | 2007 |