| Maplecroft Holdings Ltd | Construction | 2025 |
| Maplesden Construction Group Ltd | Construction | 2025 |
| Mapleview Projects Ltd | Construction | 2025 |
| Mapleview Property Solutions Ltd | Real estate | 2025 |
| Maptech Pro Ltd | Professional & scientific | 2018 |
| Maranga Ltd | Professional & scientific | 2022 |
| Marble & Granite Cutting Centre Limited | Wholesale & retail | 2018 |
| Marble Index Limited | Real estate | 2022 |
| Marc Bassett Limited | Information & communication | 2009 |
| Marcclaud Home Services Limited | Construction | 2025 |
| Marchington Solar Limited | Energy | 2013 |
| Marcussanderson.Com Limited | Information & communication | 2009 |
| Margate PV Limited | Energy | 2014 |
| Margin Syndicate Limited | Financial services | 2020 |
| Marian Global Limited | Administrative & support | 2024 |
| Marigold House Limited | Households | 2004 |
| Mariko Tsuchiyama Ltd | Manufacturing | 2020 |
| Mariston Property Ltd | Construction | 2026 |
| Maritime Staff Travel Limited | Hospitality | 2014 |
| Marj Holdings Ltd | Real estate | 2021 |
| Mark Bellringer Associates Ltd. | Professional & scientific | 2016 |
| Mark BENNETT1 Ltd | Real estate | 2013 |
| Mark Fincham Painter & Decorator Ltd | Construction | 2014 |
| Mark Garlick Words and Pictures Limited | Administrative & support | 2006 |
| Mark Hayward Accountants Limited | Professional & scientific | 2003 |
| Mark Heath Consultancy Limited | Information & communication | 2021 |
| Mark Irlam Design Ltd | Professional & scientific | 2016 |
| Mark Nightingale (UK) Ltd | Information & communication | 2014 |
| Mark One Productions Limited | Information & communication | 2024 |
| Mark Pugson Ltd | Manufacturing | 2021 |
| Mark S G Enterprises Limited | Professional & scientific | 2005 |
| Mark Tennis Ltd | Education | 2014 |
| Mark Vessey Photography Limited | Professional & scientific | 2019 |
| Marked Improvements (UK) Limited | Construction | 2013 |
| Market Alley Artisan Foods Ltd | Hospitality | 2012 |
| Marketing 101 Ltd | Information & communication | 2020 |
| Marks Motors Ltd | Wholesale & retail | 2021 |
| Marlborough Travel Ltd | Administrative & support | 2021 |
| Marlin Digital Technology Limited | Wholesale & retail | 2000 |
| Marlin Partnership Limited | Information & communication | 2000 |
| Marlipin Limited | Information & communication | 2016 |
| Marnock Place Management Company Limited | Households | 2006 |
| Marondera Investments Limited | Real estate | 2009 |
| Marondera Properties Limited | Real estate | 2009 |
| Marquee MEN Limited | Other services | 1997 |
| Marquess Consulting Limited | Professional & scientific | 2019 |
| Marrocco's Ice Cream Ltd | Hospitality | 2012 |
| Marsden Advisors Limited | Administrative & support | 2012 |
| Marsh RPF Ltd | Administrative & support | 2022 |
| Marshopper Limited | Transport & logistics | 2002 |
| Martha Property Sussex Limited | Real estate | 2021 |
| Martin Carpentry and Joinery Ltd | Construction | 2020 |
| Martin Coburn Associates Limited | Administrative & support | 2008 |
| Martin Dowd Productions Limited | Information & communication | 2006 |
| Martin Lunn Limited | Real estate | 2021 |
| Martin Mccurdy Architecture Limited | Real estate | 2012 |
| Martin Thompson Studios Ltd | Other services | 1997 |
| Martina Jane Macauley Limited | Extraterritorial | 2022 |
| Martlets Estate Management Company Limited | Households | 1967 |
| Marwaha Associates Limited | Health & social care | 2020 |
| Marylebone Tea Company Limited | Manufacturing | 2025 |
| Marzan International Ltd | Wholesale & retail | 2018 |
| Marzan London Ltd | Administrative & support | 2018 |
| MAS Software Limited | Information & communication | 2014 |
| MAS TWS Ltd | Information & communication | 2019 |
| Masbro Investments Limited | Real estate | 2006 |
| Mascoll Properties Limited | Real estate | 1964 |
| Mascot Pictures Limited | Information & communication | 1997 |
| Mason Beechwood Ltd | Professional & scientific | 2005 |
| Mason Decorating Limited | Construction | 2013 |
| Mason Projects (Brighton) Ltd | Hospitality | 2012 |
| Mason Projects (Hove) Ltd | Real estate | 2023 |
| Masscognition Ltd | Information & communication | 2026 |
| Massenka Limited | Health & social care | 2016 |
| Massip LLP | | 2014 |
| Masterfine Properties Limited | Households | 1995 |
| Mastering Management Ltd | Education | 2017 |
| Masters Graphic Solutions Ltd | Manufacturing | 2019 |
| Masterwork Films Ltd | Information & communication | 2024 |
| Masvingo Properties Limited | Real estate | 2009 |
| Matec-Global LLP | | 2009 |
| Matelco LLP | | 2008 |
| Mates Lets Limited | Real estate | 2020 |
| Mathos Consult Limited | Administrative & support | 2010 |
| Maths Focus Ltd | Education | 2010 |
| Matrix Marketing Limited | Professional & scientific | 1985 |
| Matrix Mobiles Limited | Information & communication | 2003 |
| Matt Ingham Camera Services Limited | Information & communication | 2020 |
| Matt Wasserberg Consulting Ltd | Information & communication | 2024 |
| Matthew James Consulting Limited | Administrative & support | 2007 |
| Mattjam Properties Ltd | Real estate | 2024 |
| Maven Expert Consultancy Limited | Administrative & support | 2025 |
| Mavoda LLP | | 2008 |
| Mawbray Computer Consultants Limited | Information & communication | 1994 |
| MAX Furniture Ltd | Wholesale & retail | 2008 |
| Max'D OUT Ltd | Hospitality | 2025 |
| Maxella Group Ltd | Real estate | 2026 |
| Maxella Properties Ltd | Real estate | 2022 |
| Maxicorp Ltd | Real estate | 2025 |
| Maximus Solutions Ltd | Administrative & support | 2022 |