| Meta-Leadership Consulting Limited | Information & communication | 2021 |
| Mete Films UK Ltd | Information & communication | 2016 |
| Method Media Limited | Professional & scientific | 2012 |
| Metrolec Electrical Building Services Limited | Extraterritorial | 2012 |
| Metromec Holdings Limited | Professional & scientific | 2005 |
| Metromec Mechanical Building Services Limited | Extraterritorial | 2012 |
| Metromec Services and Maintenance Limited | Construction | 2001 |
| Metset Group Ltd | Health & social care | 2023 |
| MFV Star Ltd | Manufacturing | 2021 |
| MG Five | Professional & scientific | 2007 |
| MGC Homes Limited | Real estate | 2019 |
| MGI Midgley Snelling LLP | | 2012 |
| MGI Regions Limited | Professional & scientific | 2025 |
| MGI Worldwide Limited | Professional & scientific | 2015 |
| MH Hants Limited | Health & social care | 2010 |
| Mhcg Consulting Limited | Professional & scientific | 2017 |
| MHG (London) Limited | Professional & scientific | 2011 |
| Mi-Portal Ltd | Information & communication | 2015 |
| Michael James Autos PLC | Wholesale & retail | 1974 |
| Michael Powell Limited | Financial services | 2014 |
| Mici Brothers Limited | Construction | 2005 |
| Micromed Electronics Limited | Wholesale & retail | 1995 |
| Midach Limited | Real estate | 2019 |
| Midlands Estates and Equity Ltd | Real estate | 2023 |
| Mijo Healthcare Limited | Administrative & support | 2016 |
| Mikelia Limited | Professional & scientific | 2018 |
| Millbank Group Limited | Construction | 2017 |
| Millbank Homes (Chalfont) Limited | Construction | 2017 |
| Millbank Homes (Croydon) Limited | Construction | 2018 |
| Millbank Homes (Kent) Limited | Construction | 2018 |
| Millbank Homes (North London) Limited | Construction | 2018 |
| Millbank Homes Limited | Construction | 2014 |
| Millbank Land Academy Limited | Education | 2017 |
| Millbank Land Limited | Construction | 2003 |
| Millbank Property Development Partners Limited | Extraterritorial | 2014 |
| Millbank Property Partnerships Limited | Extraterritorial | 2014 |
| Millbank Stratis Homes London Limited | Construction | 2021 |
| Millia London Limited | Wholesale & retail | 2021 |
| Millway Shippers Limited | Other services | 1965 |
| Minbar Ltd | Wholesale & retail | 2021 |
| Mint Broadlands Limited | Real estate | 2021 |
| Mint Place Ltd | Real estate | 2020 |
| Mint Share Limited | Real estate | 2025 |
| Minter Talent Ltd | Arts & recreation | 2024 |
| Mintiers Capital Ltd | Information & communication | 2026 |
| MINUS8.COM Ltd | Professional & scientific | 2024 |
| Mirabelle London Limited | Administrative & support | 2017 |
| Mirago Limited | Manufacturing | 1999 |
| Mirago M3 Ltd | Professional & scientific | 2012 |
| Mirago Technologies Limited | Information & communication | 1987 |
| Mitchell Construction & Landscaping Limited | Construction | 2018 |
| Mjcl Consultancy Limited | Professional & scientific | 2014 |
| MJP Consultancy & Sales Ltd | Professional & scientific | 2019 |
| MK Build Limited | Construction | 2011 |
| MK Enterprises London Limited | Wholesale & retail | 2017 |
| Mkat LLP | | 2024 |
| ML Atelier Ltd | Wholesale & retail | 2025 |
| MLM Concerts Limited | Administrative & support | 2009 |
| MM3 Molly Millars Lane Management Company Limited. | Extraterritorial | 2002 |
| Mmpt Ltd | Financial services | 2020 |
| MMV Enterprises Limited | Real estate | 2026 |
| Mmxx AD UK Limited | Extraterritorial | 2020 |
| Model Logic Limited | Administrative & support | 1988 |
| Modern Profiles Limited | Wholesale & retail | 2001 |
| Moderna Properties Ltd | Real estate | 2016 |
| Modular Design Studio Ltd | Professional & scientific | 2025 |
| Modulus SI Investments Ltd | Professional & scientific | 2024 |
| Modulus SI Ltd | Information & communication | 2018 |
| Mojok Limited | Real estate | 2023 |
| Molesey Boathouse Limited | Extraterritorial | 2019 |
| Mondi Aberdeen Limited | Administrative & support | 1990 |
| Mondi Consumer Goods Packaging UK Ltd | Manufacturing | 2004 |
| Mondi Finance PLC | Financial services | 2006 |
| Mondi Investments Limited | Professional & scientific | 2004 |
| Mondi Packaging (Delta) Limited | Professional & scientific | 1964 |
| Mondi Packaging UK Holdings Limited | Professional & scientific | 1999 |
| Mondi Pension Trustee Limited | Professional & scientific | 2008 |
| Mondi PLC | Professional & scientific | 2007 |
| Mondi Scunthorpe Limited | Manufacturing | 1979 |
| Mondi Services (UK) Limited | Administrative & support | 2006 |
| Monojack Ltd. | Construction | 1998 |
| Montii Ltd | Arts & recreation | 2025 |
| Montpelier Holdings Limited | Other services | 2019 |
| Montpelier Portfolio Limited | Financial services | 2019 |
| Montpelier Properties Limited | Real estate | 2010 |
| Montreaux Build Limited | Construction | 2016 |
| MOO D Blue Ltd | Administrative & support | 2022 |
| Moonbyte Limited | Information & communication | 1996 |
| Moonshot Investments Limited | Administrative & support | 2017 |
| Morariho Limited | Wholesale & retail | 2024 |
| Morgan Capital Assets Ltd | Financial services | 2022 |
| Morrill Property INV. Limited | Construction | 1987 |
| Morrison Street Properties Limited | Real estate | 2003 |
| Morus Developments Ltd | Construction | 2020 |
| Moss Coaching Associates Limited | Professional & scientific | 2018 |
| Mostyn Investments Ltd | Real estate | 2021 |
| Mostyn Retail Ltd | Real estate | 2024 |
| Motion View Media Ltd | Manufacturing | 2023 |
| Motor Record Limited | Information & communication | 2013 |
| Motor-People Limited | Wholesale & retail | 2008 |