| Mary Keeley Consultancy Limited | Professional & scientific | 2010 |
| Maseko Ltd | Health & social care | 2022 |
| Master Solutions Development Limited | Professional & scientific | 2009 |
| Matchpoint Service Limited | Arts & recreation | 2002 |
| Mathengine Limited | Administrative & support | 1997 |
| Matrix Aesthetics Limited | Wholesale & retail | 2026 |
| Matrix Footwear Limited | Wholesale & retail | 2007 |
| Matrix UK Holdings Trustee Limited | Professional & scientific | 2024 |
| Matt Jones CRE8MEDIA Limited | Information & communication | 2013 |
| Matt on Malt Limited | Hospitality | 2008 |
| Matt Peel & Co Limited | Information & communication | 2023 |
| Matt WJ Hunt Ltd | Administrative & support | 2021 |
| Matthew Austin Limited | Construction | 2004 |
| Mattozone Ltd | Wholesale & retail | 2023 |
| MAX Scaffold Products Ltd | Manufacturing | 2012 |
| MAX2PRODUCTS Limited | Manufacturing | 2017 |
| Maximal Search Ltd | Administrative & support | 2025 |
| Mayfair Independent Limited | Financial services | 1999 |
| Mayflower Productions Limited | Arts & recreation | 2005 |
| MB3D Limited | Professional & scientific | 2012 |
| MBA Information Technology Holdings Limited | Financial services | 2013 |
| Mccartney Sport Horses Ltd | Agriculture & fishing | 2021 |
| Mccooey Engineering Limited | Manufacturing | 2003 |
| Mccooey Limited | Manufacturing | 2012 |
| Mchardy Design Limited | Professional & scientific | 2004 |
| Mcintosh Safety Consultancy Limited | Professional & scientific | 2014 |
| Mcjr Consulting Ltd | Professional & scientific | 2014 |
| MCM Groundworks Limited | Construction | 2017 |
| MCP Pubs Ltd | Hospitality | 2012 |
| Mdaxx Ltd | Professional & scientific | 2021 |
| Mdkcleaning Ltd | Administrative & support | 2017 |
| Meadex Holdings Ltd | Financial services | 2022 |
| Meadex Technical & Medical Mouldings Limited | Financial services | 2024 |
| Meat London Holdings Limited | Financial services | 2026 |
| Meat London Limited | Hospitality | 2011 |
| Meck Foods Ltd | Wholesale & retail | 2024 |
| Medarkive Ltd | Information & communication | 2013 |
| Media Delicious Limited | Information & communication | 2008 |
| Medicine in Motion Ltd | Health & social care | 2024 |
| Medicolegaleye Limited | Health & social care | 2015 |
| Medimole Limited | Health & social care | 2025 |
| Medmix AHP UK Ltd | Professional & scientific | 2025 |
| Meerstar Limited | Hospitality | 2020 |
| MEG Professional Services Ltd | Construction | 2025 |
| Mellow Jersey Limited | Administrative & support | 2016 |
| Melville House Capital Limited | Professional & scientific | 2026 |
| Meon Pilates Limited | Other services | 2017 |
| Meon Treats Ltd | Wholesale & retail | 2023 |
| Mercers Croft Limited | Real estate | 2017 |
| Merch Branding Limited | Administrative & support | 2020 |
| Merchandise Branding Limited | Administrative & support | 2012 |
| Mercia Properties Group Ltd | Real estate | 2021 |
| Merestone Limited | Real estate | 2001 |
| Merlin Scott Associates Limited | Information & communication | 1993 |
| Meru Today Limited | Professional & scientific | 2022 |
| Metaxiom Holdings Limited | Professional & scientific | 2021 |
| Metrictechmanagement Ltd | Information & communication | 2026 |
| MF Medico-Legal Ltd | Health & social care | 2025 |
| MFA 3 Limited | Extraterritorial | 2016 |
| MFC Dannebrog Limited | Financial services | 2021 |
| MFC Group (UK) Ltd | Wholesale & retail | 2004 |
| MGC Care Limited | Health & social care | 2012 |
| MGT Accounting Limited | Professional & scientific | 2017 |
| Mhgraphics Limited | Professional & scientific | 1995 |
| MI Education Ltd | Education | 2025 |
| Microvar Limited | Information & communication | 1962 |
| Midas Pet Products Limited | Administrative & support | 2002 |
| Midland Home Investments Ltd | Real estate | 2024 |
| Midland Property Solutions Limited | Construction | 2005 |
| Midland Real Estates Limited | Real estate | 2003 |
| Midsummer Garden Ltd | Hospitality | 2022 |
| Miitera Technologies Ltd | Information & communication | 2020 |
| Mike Murphy Consulting Limited | Professional & scientific | 2012 |
| Mila Property Group Ltd | Construction | 2021 |
| Milcote Close (Welford) Management Company Limited | Households | 2019 |
| Mill Field Grange Management Limited | Households | 1999 |
| Mill Sales Direct Limited | Wholesale & retail | 2012 |
| Millbank Technologies Limited | Information & communication | 2025 |
| Millers Close (Welford-On-Avon) Management Co Ltd | Real estate | 2026 |
| Mindworks Therapy Centre Ltd | Health & social care | 2026 |
| Minerva Performance Consulting Ltd | Professional & scientific | 2024 |
| Ming Garden Foods Limited | Hospitality | 2021 |
| Mini Mudders Ltd | Professional & scientific | 2022 |
| Mini Star Shop Ltd | Wholesale & retail | 2025 |
| Mioc Limited | Professional & scientific | 2018 |
| Miracapital Limited | Real estate | 2018 |
| Miramar Touring Co Ltd | Administrative & support | 2020 |
| Mishora Wholesale Ltd | Wholesale & retail | 2026 |
| Misura Gallery Limited | Wholesale & retail | 2024 |
| Mitchelectronics Ltd | Manufacturing | 2022 |
| Mitchelectronics Media Ltd | Information & communication | 2022 |
| Mixed Farms Limited | Real estate | 1948 |
| MK Cleaning Group Limited | Wholesale & retail | 2025 |
| MLB Business Services Limited | Professional & scientific | 2022 |
| Mlwh Limited | Professional & scientific | 2011 |
| Mmra Accountancy Ltd | Professional & scientific | 2023 |
| MO Fitness Limited | Arts & recreation | 2019 |
| MO Scandinavia Ltd | Professional & scientific | 2018 |
| Mocanu Nicusor Ltd | Transport & logistics | 2024 |
| Mocha Investments Ltd | Real estate | 2016 |