| Many Rooms Limited | Real estate | 2012 |
| MAP Top Care Ltd | Health & social care | 2019 |
| Mapeex Ltd | Administrative & support | 2013 |
| Maplango Limited | Professional & scientific | 2022 |
| Maple Forge Limited | Manufacturing | 2019 |
| Maplehurst Square Limited | Real estate | 2024 |
| Maplehurst Square Properties Ltd | Real estate | 2025 |
| Maplescene Limited | Administrative & support | 2014 |
| Maplewood Court Management Company Limited | Real estate | 2006 |
| Marc Samuels Limited | Wholesale & retail | 2016 |
| Marchan Limited | Administrative & support | 2019 |
| Marchel Limited | Professional & scientific | 2021 |
| Marchesi Farming Limited | Professional & scientific | 1997 |
| Marcura Payments Group Ltd | Financial services | 2025 |
| Marcura UK Limited | Administrative & support | 2015 |
| Margin Services Limited | Wholesale & retail | 2002 |
| Mariam Moments Ltd | Professional & scientific | 2026 |
| Marie Jose Gallery Limited | Wholesale & retail | 2021 |
| Marik Mews Limited | Households | 1994 |
| Marina Way Parking Ltd | Other services | 2014 |
| Marine Biology Posters Ltd | Wholesale & retail | 2025 |
| Marine Dental Holdings Ltd | Health & social care | 2020 |
| Marine Dental Practice Limited | Health & social care | 2010 |
| Marine House Brighton RTM Ltd | Households | 2008 |
| Marine House Goring Ltd | Households | 2020 |
| Marine Parade Worthing LLP | | 2025 |
| Marine Services (MS) Limited | Administrative & support | 2019 |
| Marinus Artis Ltd | Professional & scientific | 2016 |
| Mariposita Ltd | Construction | 2022 |
| Mariquecalcus Ltd | Information & communication | 2012 |
| Marius International Holding Limited | Financial services | 2020 |
| Mark & Taryn Taylor LLP | | 2023 |
| Mark Douglas Roofing Limited | Construction | 2002 |
| Mark One Training Limited | Education | 2014 |
| Mark Rubinstein Limited | Arts & recreation | 2000 |
| Mark Smith Media Limited | Professional & scientific | 2014 |
| Mark Swindells Consultancy Ltd | Professional & scientific | 2020 |
| Mark Welton Limited | Real estate | 2020 |
| Market Dog Limited | Administrative & support | 2017 |
| Market Drive Media Ltd | Information & communication | 2026 |
| Market Town Developments Limited | Administrative & support | 2010 |
| Market Town Foods Limited | Administrative & support | 2010 |
| Market Town Group Limited | Financial services | 2025 |
| Marketing Delivery Limited | Administrative & support | 2007 |
| Marketing Hounds Limited | Information & communication | 2023 |
| Marketing Modular Ltd | Administrative & support | 2024 |
| Marketing Ways Ltd | Administrative & support | 2019 |
| Marla Rose Properties Ltd | Real estate | 2024 |
| Marlands Park Limited | Construction | 2013 |
| Marlborough Court Freehold Company Limited | Real estate | 2004 |
| Marlborough Court Freehold Partners LLP | | 2007 |
| Marlex Orias Limited | Health & social care | 2014 |
| Marley Kitchens Limited | Construction | 2018 |
| Marley Property Investments Limited | Real estate | 2018 |
| Marley Worthing Ltd | Hospitality | 2025 |
| Marlin Capital Europe Limited | Financial services | 2002 |
| Marlin Europe I Limited | Administrative & support | 2006 |
| Marlin Europe II Limited | Administrative & support | 2007 |
| Marlin Europe V Limited | Financial services | 2012 |
| Marlin Europe VI Limited | Financial services | 2012 |
| Marlin Unrestricted Holdings Limited | Professional & scientific | 2013 |
| Marlowe Electrical Ltd | Construction | 2023 |
| Marlowe Marketing Limited | Professional & scientific | 2021 |
| Marmont Developments Limited | Construction | 2004 |
| Marmont Holdings Limited | Financial services | 2019 |
| Marmoris LLP | | 2021 |
| Marron Design Limited | Administrative & support | 2013 |
| Marshall Clark Estates Limited | Real estate | 2026 |
| Marshall Clark LLP | | 2003 |
| Martello Property Investments Limited | Real estate | 2017 |
| Martin Levy Commercial Ltd. | Real estate | 2003 |
| Martin Satchell Surveys Ltd | Other services | 2018 |
| Martin Snowdon Limited | Wholesale & retail | 2009 |
| Martlet Audit Limited | Professional & scientific | 2000 |
| Mary Myatt Learning Limited | Education | 2011 |
| Maryamhofu Ltd | Hospitality | 2023 |
| MAS and Associates Ltd | Professional & scientific | 2012 |
| Masala Club Ltd | Hospitality | 2025 |
| Mascot Travels Limited | Administrative & support | 2024 |
| Mash Manors Limited | Real estate | 2026 |
| Massage Spaces Ltd | Other services | 2019 |
| Massie Properties Limited Liability Partnership | | 2009 |
| Masterisk Limited | Information & communication | 2019 |
| Masters Roofing and Construction Ltd | Construction | 2024 |
| Masthead Properties Limited | Real estate | 2017 |
| Matches Limited | Extraterritorial | 1983 |
| Material Environmental Limited | Construction | 2025 |
| Matrix Foods Limited | Wholesale & retail | 2000 |
| Matt Abbott Poet Ltd. | Arts & recreation | 2016 |
| Matt Gallagher Media Limited | Financial services | 2023 |
| Matthew Anthony Ltd | Real estate | 2018 |
| Matthew Cooper Property Consultancy Ltd | Administrative & support | 2013 |
| Matthew Davey Gardens Limited | Administrative & support | 2018 |
| Matthew Parratt Associates Limited | Professional & scientific | 2014 |
| MAX Murphy Consulting Limited | Professional & scientific | 2022 |
| Maxco Chartering LLP | | 2021 |
| Maxco Limited | Professional & scientific | 2008 |
| Maxgfx Ltd | Information & communication | 2019 |
| Maxicare Healthcare Ltd | Administrative & support | 2017 |
| Maxida Medical Limited | Health & social care | 2026 |