| MBF (Sussex) Limited | Professional & scientific | 2026 |
| Mbjs Developments Ltd | Construction | 2012 |
| MC Indian Cuisine Ltd | Hospitality | 2025 |
| MC Property Maintenance Ltd | Construction | 2001 |
| Mcado Limited | Professional & scientific | 2026 |
| Mcbride Motor Group Limited | Wholesale & retail | 2023 |
| Mcdonald Lynch Ltd. | Real estate | 1994 |
| Mcevoy Marshall Arts Ltd | Other services | 2025 |
| Mcewen & Co Limited | Professional & scientific | 2003 |
| Mcfaul Limited | Other services | 2004 |
| MCK Catering Events Ltd | Hospitality | 2024 |
| Mclaren-Barnsby Ltd | Professional & scientific | 2023 |
| Mcleod Painting Contractors Limited | Construction | 2024 |
| Mcmatt & Co Limited | Other services | 2024 |
| MCN Services Limited | Financial services | 2019 |
| Mcsons Property Ltd | Real estate | 2019 |
| MD Interior Projects Limited | Construction | 2005 |
| Md-Contracting (Southern) Ltd | Construction | 2025 |
| MDA Decorators Ltd | Construction | 2021 |
| Mdmpjs Limited | Arts & recreation | 2025 |
| MDR Polo Limited | Arts & recreation | 2021 |
| Mdwra Ltd | Households | 2017 |
| Meadow Orchard Limited | Wholesale & retail | 2006 |
| Meadowgate Construction Limited | Construction | 2013 |
| Meadowgate Shepherds Huts Limited | Hospitality | 2022 |
| Meadowlands Management Company Limited | Administrative & support | 2005 |
| Meadrock (West Sussex) Limited | Wholesale & retail | 2025 |
| Meadrock Holdings Limited | Financial services | 2025 |
| Meadrock Limited | Wholesale & retail | 1971 |
| Meadway Architectural Design Ltd. | Professional & scientific | 2016 |
| Measured Works Limited | Professional & scientific | 2008 |
| Mechanical Technical Services Limited | Administrative & support | 1998 |
| Medescape Limited | Hospitality | 2010 |
| Medex Research Limited | Health & social care | 2001 |
| Medflow Clinical Ltd | Transport & logistics | 2019 |
| Medhursts Commercial Surveyors Limited | Professional & scientific | 2014 |
| Mediapreneur Ltd | Professional & scientific | 2023 |
| Mediator Network Ltd | Administrative & support | 2016 |
| Medic Technologies Ltd | Health & social care | 2021 |
| Medical Aesthetix Ltd | Health & social care | 2019 |
| Medical Leaf Ltd | Information & communication | 2026 |
| Medical Select LLP | | 2010 |
| Mediluxe Clinic Ltd | Other services | 2026 |
| Medina Contracts Limited | Construction | 2001 |
| Mediquill Ltd | Professional & scientific | 2017 |
| Medlams Surveys Limited | Professional & scientific | 2013 |
| Meechans Limited | Financial services | 2025 |
| Megawatt Coaching Ltd | Professional & scientific | 2015 |
| Meha Developments Limited | Real estate | 2021 |
| Meliad Medical Ltd | Professional & scientific | 2010 |
| Melisshair Ltd | Other services | 2017 |
| Mellon Developments Ltd | Information & communication | 2021 |
| Melvyn Vincent Associates Limited | Professional & scientific | 1999 |
| Mensted Limited | Professional & scientific | 1987 |
| Mentor Media Ltd | Information & communication | 2021 |
| MER Ltd | Professional & scientific | 2007 |
| Mercan Accounting and Consultancy Ltd | Professional & scientific | 2024 |
| Merchant Distribution Limited | Wholesale & retail | 2016 |
| Meridian Electrical Ltd | Construction | 2005 |
| Merriemead Limited | Financial services | 2020 |
| Merriman Software Solutions Ltd | Information & communication | 2025 |
| Merritown Farm Limited | Real estate | 2024 |
| Merritown Park Limited | Arts & recreation | 2024 |
| Merry Meats Limited | Hospitality | 2006 |
| Merryhill Mushrooms Limited | Agriculture & fishing | 2006 |
| Merrymeet Limited | Professional & scientific | 1997 |
| Merstone Barn Ltd | Construction | 2026 |
| Messy Lets Ltd | Real estate | 2018 |
| Metafact Limited | Information & communication | 2004 |
| Method Construction Services Ltd | Construction | 2023 |
| Metswift Data Ltd | Information & communication | 2016 |
| Metswift Holdings Ltd | Professional & scientific | 2019 |
| Metswift IP Ltd | Information & communication | 2016 |
| Metswift Services Ltd | Professional & scientific | 2015 |
| Metz Brothers Builders Limited | Construction | 2018 |
| Meyerhealth Ltd | Health & social care | 2008 |
| Meynell Hayes Limited | Professional & scientific | 2022 |
| MG & SON Ltd | Administrative & support | 2016 |
| MGA RTM Company Limited | Households | 2026 |
| MGD RTM Company Ltd | Households | 2025 |
| MGD Specialist Interior Finishes Ltd | Construction | 2018 |
| Mgdsif EOT Trustee Limited | Financial services | 2025 |
| Mgdsif Holdings Ltd | Construction | 2019 |
| MGM Trades Ltd | Manufacturing | 2025 |
| MGS Contractors Ltd | Administrative & support | 2014 |
| MGV Tech Ltd | Information & communication | 2026 |
| MH Architects Limited | Professional & scientific | 1986 |
| MH Builders Limited | Construction | 2003 |
| MI Home Living Ltd | Wholesale & retail | 2019 |
| Micca Limited | Financial services | 2014 |
| Michael Glanville Executive Coaching Limited | Administrative & support | 2024 |
| Michael Jones Plumbing Limited | Construction | 2013 |
| Michael Taylor Architects Limited | Professional & scientific | 2015 |
| Michelle Jones Aesthetics Ltd | Other services | 2018 |
| Micouk Ltd | Administrative & support | 2018 |
| Middle Barton Properties Limited | Real estate | 2016 |
| Midhurst Plumbers Ltd | Construction | 2023 |
| Midlife Mojo Limited | Administrative & support | 2014 |
| MIG Investments Ltd | Financial services | 2021 |
| Migra Data Limited | Information & communication | 2023 |