| Maximus &ME Ltd | Health & social care | 2025 |
| Maxrana Ltd | Real estate | 2019 |
| Maxwells Events Ltd | Hospitality | 2026 |
| Maya Beauty Clinic Limited | Health & social care | 2021 |
| Maybrook Limited | Real estate | 1993 |
| MB Estate Holdings Ltd | Financial services | 2025 |
| MB Motorworks Ltd | Wholesale & retail | 2014 |
| MB Worthing Ltd | Hospitality | 2025 |
| MBD Developments Limited | Construction | 2019 |
| MBK Media Limited | Information & communication | 2022 |
| MBP Media Limited | Information & communication | 2015 |
| MBP Trading Ltd | Manufacturing | 2005 |
| Mbsjq Limited | Arts & recreation | 2021 |
| MBY Training and Consultancy Ltd | Professional & scientific | 2014 |
| MC Creations Ltd | Manufacturing | 2026 |
| MC FLY Enterprises Limited | Administrative & support | 2006 |
| MC Property Development (Sussex) Ltd | Construction | 2006 |
| MC Sales and Lettings Limited | Real estate | 2025 |
| Mcbe Ltd | Financial services | 2026 |
| Mccarthy Food Group Ltd | Hospitality | 2026 |
| Mccorquodale Holdings CIC | Arts & recreation | 2025 |
| Mccoubrey Ltd | Construction | 2025 |
| MCE Portfolio Limited | Administrative & support | 2006 |
| Mcentegart Holdings Ltd | Real estate | 2021 |
| Mcgowan Keane Ltd | Information & communication | 2018 |
| Mckechnie Aviation Ltd. | Professional & scientific | 2014 |
| Mckinnie Ltd | Wholesale & retail | 2025 |
| MCM Haus Limited | Wholesale & retail | 2021 |
| Mcml Financial Limited | Other services | 2013 |
| MCR Property Limited | Real estate | 2017 |
| MCR Ventures Ltd | Information & communication | 2013 |
| MD Growth Advisory Ltd | Professional & scientific | 2025 |
| MD Hants Limited | Hospitality | 2015 |
| MD Nail Worthing Ltd | Other services | 2023 |
| MD Nails Worthing Ltd | Other services | 2026 |
| MD Sports (Sussex) Ltd | Administrative & support | 2019 |
| MDB Land & Estates Limited | Real estate | 2025 |
| MDB Productions Limited | Arts & recreation | 2019 |
| MDK Digital Ltd | Information & communication | 2025 |
| Mdtl Ltd | Hospitality | 2020 |
| ME III Limited | Administrative & support | 2010 |
| ME IV Limited | Administrative & support | 2010 |
| Meachin's Merch Ltd | Wholesale & retail | 2025 |
| Meadow Gate Estate Limited | Households | 2025 |
| Meadvale Homes Limited | Construction | 2005 |
| Meadvale Redhill Management Company Ltd | Households | 2008 |
| Mealgo Limited | Hospitality | 2026 |
| Meaningbit Ltd | Information & communication | 2017 |
| Mechatronic Engineering Resources Ltd | Manufacturing | 2022 |
| MED Kitchen Worthing Ltd | Hospitality | 2026 |
| Medcalf Plumbing & Heating Limited | Construction | 2021 |
| Media Building Ltd | Professional & scientific | 2000 |
| Media Scotica Limited | Information & communication | 2022 |
| Media Services Sussex Limited | Construction | 1989 |
| Mediachum Limited | Information & communication | 2011 |
| Mediapack Limited | Professional & scientific | 2003 |
| Mediatriangle Limited | Information & communication | 2021 |
| Medical Research Limited | Extraterritorial | 2023 |
| Medicare Training Limited | Other services | 2010 |
| Medina Credit Management Limited | Administrative & support | 2005 |
| Medindex Ltd | Health & social care | 2019 |
| Medius Vinea Limited | Real estate | 2022 |
| Medius XV Limited | Real estate | 2017 |
| Medrose Minver Limited | Professional & scientific | 2020 |
| Medville Limited | Households | 1997 |
| Meed's Aviation and Marine Services Ltd | Manufacturing | 2026 |
| Meet Minds UK CIC | Other services | 2024 |
| Megaloop Ltd | Administrative & support | 2014 |
| Megapixel Screen Displays Limited | Administrative & support | 2015 |
| Meica Solutions Ltd | Professional & scientific | 2022 |
| Meireles & Harras Properties Ltd | Real estate | 2024 |
| Mekra Lang United Kingdom Limited | Extraterritorial | 2016 |
| Mekra UK Limited | Wholesale & retail | 2008 |
| Mekratronics UK Limited | Extraterritorial | 2017 |
| Melanie Jade Design Ltd | Professional & scientific | 2020 |
| Mellor & Co Property Ltd | Real estate | 2025 |
| Melrose Care Limited | Health & social care | 2004 |
| Melt Properties Ltd | Real estate | 2021 |
| Melville Thirteen Properties Ltd | Real estate | 2024 |
| Memrina Ltd | Hospitality | 2025 |
| Mendac Property Services Limited | Real estate | 2021 |
| Mendes Health Care Limited | Health & social care | 2015 |
| Mending Fences CIC | Health & social care | 2024 |
| Mennel UK Limited | Administrative & support | 2021 |
| Meow Nails Ltd | Other services | 2025 |
| Mera Ventures Limited | Financial services | 2023 |
| Mercader Solutions Ltd | Wholesale & retail | 2016 |
| Merchandise by Valand Limited | Manufacturing | 2024 |
| Merchants Global Limited | Financial services | 2012 |
| Meredith Financial Planning Ltd | Professional & scientific | 2020 |
| Meredith Project Consulting Ltd | Administrative & support | 2019 |
| Merill Properties LLP | | 2023 |
| Merill UK Limited | Administrative & support | 2024 |
| Merlin Buffet Systems Ltd | Wholesale & retail | 2010 |
| Merling Care Limited | Financial services | 2018 |
| Merna Properties Ltd | Real estate | 2020 |
| Merritt Lease Holdings Limited | Real estate | 2020 |
| Merryfield Limited | Real estate | 2026 |
| Mesh Community Limited | Information & communication | 2026 |
| Metafora Limited | Extraterritorial | 2014 |