| MASH24FIT Ltd | Health & social care | 2024 |
| Mason & Deen Consultancy Limited | Information & communication | 2017 |
| Masses Limited | Information & communication | 2005 |
| Mastercraft Shutters Limited | Construction | 2022 |
| Masterpiece Landscaping Ltd | Professional & scientific | 2025 |
| Masters and Ashby Construction Ltd | Construction | 2025 |
| Match Fit Community Limited | Education | 2026 |
| Mathieson & SON Ltd | Real estate | 2018 |
| Matrix 24 Limited | Construction | 2003 |
| Matrix Security Ltd | Administrative & support | 2019 |
| Matt Clark Associates Limited | Professional & scientific | 2014 |
| Matt Glen Limited | Information & communication | 2011 |
| Matte Black London Ltd | Information & communication | 2020 |
| Maverick Arts Publishing Limited | Information & communication | 2008 |
| Maverick Pictures Ltd | Information & communication | 2025 |
| MAX Chance Design Limited | Professional & scientific | 2023 |
| Maxcast Accountancy Ltd | Professional & scientific | 2020 |
| Maxemisso Holdings Limited | Financial services | 2025 |
| Maxima Training & Development Ltd | Administrative & support | 2003 |
| Maximillian Design Ltd | Administrative & support | 2023 |
| Maximum Information Consulting Ltd | Information & communication | 2020 |
| Maximum Information Innovation Ltd | Information & communication | 2020 |
| Maximum Information Ltd | Professional & scientific | 2020 |
| Maximum Information Services Ltd | Information & communication | 2020 |
| Maximus Health Ltd | Financial services | 2016 |
| MAY 2003 Ltd | Transport & logistics | 2023 |
| MAY Stanley Limited | Information & communication | 2013 |
| Mayes Lane Ltd | Real estate | 2022 |
| Mayfox Limited | Real estate | 2020 |
| Maynard Risk Consulting Limited | Financial services | 2021 |
| Maynes Contracting Ltd | Administrative & support | 2014 |
| Mayvin Consultants Ltd | Professional & scientific | 2023 |
| Mazarin Group Ltd | Financial services | 2018 |
| Mazarin Properties Ltd | Real estate | 2020 |
| MBY Transformation Ltd | Professional & scientific | 2022 |
| MC Leaders Ltd | Information & communication | 2025 |
| Mccabe Groundworks Limited | Wholesale & retail | 2008 |
| Mccarthy SET DEC Limited | Information & communication | 2018 |
| Mccullough Moore Limited | Administrative & support | 2005 |
| MCE Connect Limited | Information & communication | 2020 |
| Mcguigan Property Investments Limited | Real estate | 2023 |
| MCH Consultants (Horsham) Ltd | Professional & scientific | 2017 |
| Mchale Construction Ltd | Construction | 2001 |
| Mchale Contractors Limited | Construction | 2009 |
| Mcjoice International Ltd | Transport & logistics | 2025 |
| Mcsc Electrical Ltd | Construction | 2025 |
| Mcvw Limited | Information & communication | 2015 |
| MD Durant Property Ltd | Real estate | 2024 |
| MD Private Limited | Construction | 2017 |
| MDG Advisory Limited | Professional & scientific | 2019 |
| MDH Legal Costs Ltd | Professional & scientific | 2023 |
| MDR Accountancy Ltd | Professional & scientific | 2018 |
| MDR Asset Management Limited | Real estate | 2015 |
| MDR Genetics Ltd | Professional & scientific | 2020 |
| ME Entertainment London Ltd | Arts & recreation | 2022 |
| ME UK Investments 1 Ltd | Real estate | 2021 |
| ME24 Limited | Information & communication | 2025 |
| Meadowbrook (Storrington) Management Company Limited | Households | 2016 |
| Meadows Wellbeing Ltd | Extraterritorial | 2020 |
| Meat Masala (Horsham) Ltd | Wholesale & retail | 2024 |
| Mech Pro Plus Ltd | Construction | 2024 |
| Mechcool Ltd | Energy | 2014 |
| Medcommsconsult Ltd | Professional & scientific | 2009 |
| Medex Scientific (U.K.) Limited | Professional & scientific | 1997 |
| Medi World Gulf Ltd | Wholesale & retail | 2025 |
| Media Easier Ltd | Information & communication | 2019 |
| Mediacells Limited | Information & communication | 2004 |
| Medical Express (U.K.) Limited | Professional & scientific | 1981 |
| Medical Materials First Ltd | Wholesale & retail | 2023 |
| Medical Treatment Limited | Health & social care | 2019 |
| Medics Inc Ltd. | Health & social care | 2021 |
| Medioffice Limited | Information & communication | 2021 |
| Medlegal PA Limited | Administrative & support | 2018 |
| Meeplewood Limited | Manufacturing | 2023 |
| Megan and Mabel Ltd | Other services | 2024 |
| Mekong 3288 Ltd | Hospitality | 2026 |
| Mekong Limited | Hospitality | 2023 |
| Melberry Development Management Limited | Construction | 2020 |
| Melberry Investments Limited | Construction | 2020 |
| Mellifont Abbey LLP | | 2006 |
| Mellows Group Ltd | Financial services | 2022 |
| Melodie Creative Ltd | Construction | 2023 |
| Melrose Farm Holdings Ltd | Arts & recreation | 2020 |
| Mendoza Property Management Limited | Real estate | 2021 |
| Menrva Consulting Limited | Professional & scientific | 2023 |
| Menton Consulting Ltd | Information & communication | 2021 |
| Mercury Car Sales Limited | Wholesale & retail | 2016 |
| Mergel Construction Ltd. | Construction | 2014 |
| Meridian Control Systems Ltd | Construction | 2013 |
| Meridian Point Group Ltd | Wholesale & retail | 2026 |
| Merkara Consulting Ltd | Information & communication | 2026 |
| Mermoz Ltd | Professional & scientific | 2000 |
| Merrell Editions Limited | Information & communication | 2013 |
| Merrell Publishers Limited | Information & communication | 1989 |
| Merroquest Limited | Real estate | 1993 |
| Messham International Stunt Show Limited | Arts & recreation | 2009 |
| Metabolyx Health Ltd | Health & social care | 2025 |
| Metal Components Limited | Manufacturing | 1984 |
| Metatec Limited | Wholesale & retail | 1982 |
| Metersure Ltd | Manufacturing | 2025 |