| Malthouse Mews (M.C.) Limited | Households | 2021 |
| Mama's Joy Limited | Wholesale & retail | 2025 |
| Mancey Limited | Professional & scientific | 2019 |
| Mancey Property Investments Limited | Real estate | 2022 |
| Manger Care Limited | Health & social care | 2025 |
| Manntek Consulting Ltd | Information & communication | 2023 |
| Manor Farm Barns Residents Limited | Households | 2018 |
| Mapletons Management Ltd | Real estate | 2003 |
| March Doors Limited | Manufacturing | 2014 |
| March Service Limited | Other services | 2015 |
| Market Event Solutions Ltd | Hospitality | 2018 |
| Marlborough House Financial Services Ltd | Financial services | 2018 |
| Marshall Management Consulting Limited | Professional & scientific | 2020 |
| Martin Brindley PR Ltd | Professional & scientific | 2015 |
| Martinibazar Limited | Wholesale & retail | 2018 |
| Martinique Gardening Ltd | Administrative & support | 2023 |
| Marz Houses Limited | Real estate | 2024 |
| Masdar International Limited | Professional & scientific | 1978 |
| Matthew Gregory Consulting Limited | Information & communication | 2015 |
| Maxlee Group Ltd | Construction | 2014 |
| Mayes Consultants Limited | Professional & scientific | 2011 |
| Mayfield Court Management (Eversley) Limited | Households | 1992 |
| Mccomas Consulting Limited | Professional & scientific | 2012 |
| Mcgregor WYN Ltd | Real estate | 2022 |
| Mead Gardens Management Company Limited | Households | 2005 |
| Meadowset Limited | Real estate | 1991 |
| Medalstable Limited | Professional & scientific | 1987 |
| Medexpat Limited | Extraterritorial | 2000 |
| Media Energy Limited | Information & communication | 2013 |
| Medintro UK Ltd | Administrative & support | 2014 |
| Medisec Connect Ltd | Administrative & support | 2025 |
| Medivia Limited | Professional & scientific | 2023 |
| Mega Merchandising Limited | Other services | 2011 |
| Meliora Strategy Limited | Information & communication | 2023 |
| Mentor Training Academy Limited | Professional & scientific | 2013 |
| Merit Mortgages Ltd | Financial services | 2022 |
| Merronbrook Limited | Manufacturing | 1979 |
| Messenger Coaching & Consulting Limited | Professional & scientific | 2024 |
| Meteor Ltd | Wholesale & retail | 2020 |
| Metz Projects Ltd | Real estate | 2019 |
| MGC Engineering and Consultancy Limited | Professional & scientific | 2019 |
| MGM Corporation Limited | Construction | 2010 |
| MGT Creative Ltd | Professional & scientific | 2017 |
| Mhkh Engineering Ltd | Professional & scientific | 2007 |
| Michael Connolly Limited | Information & communication | 2003 |
| Mick Tott Construction Ltd. | Construction | 2006 |
| Mickael & Ludovic Limited | Other services | 2008 |
| Miiloo Limited | Education | 2025 |
| Mike Garwood Ltd | Professional & scientific | 2004 |
| Mila Associates Ltd | Professional & scientific | 2019 |
| Mindenhurst I & J Management Company Limited | Households | 2025 |
| Minna Bunting Ltd | Wholesale & retail | 2025 |
| Mistique Limited | Information & communication | 1999 |
| MJM Security Solutions Ltd | Other services | 2024 |
| MJT Accounting Services Limited | Professional & scientific | 2017 |
| MK1 Automotive Ltd | Wholesale & retail | 2021 |
| Mknx Ltd | Wholesale & retail | 2023 |
| MKR Property Holdings Ltd | Real estate | 2022 |
| MKZ Properties Limited | Extraterritorial | 2002 |
| Mmbw Ltd | Administrative & support | 2022 |
| Mmgd Limited | Manufacturing | 2015 |
| Modus Aviation Limited | Transport & logistics | 2015 |
| Mojave Specialist Motors Ltd | Wholesale & retail | 2017 |
| Monotrack Ltd | Professional & scientific | 2016 |
| Montsci Ltd | Information & communication | 2023 |
| Montu Watches Ltd | Wholesale & retail | 2022 |
| Monxton Place Residents Association Limited | Households | 2011 |
| Moonpress Limited | Arts & recreation | 1996 |
| More Than Just Ltd | Information & communication | 2025 |
| Morenow Ltd | Information & communication | 2015 |
| Morgan Property Enhancement Ltd | Construction | 2022 |
| Mortuary Equipment Direct Limited | Other services | 2019 |
| Motohaus Powersports Limited | Wholesale & retail | 1997 |
| Mount View Enterprises Ltd | Agriculture & fishing | 2025 |
| Moutan Limited | Wholesale & retail | 2007 |
| Mowmate Limited | Manufacturing | 2009 |
| MPB Professional Services Limited | Professional & scientific | 2014 |
| MSF Historical Restoration Ltd | Construction | 2020 |
| MSP Associates Limited | Professional & scientific | 2005 |
| MT Integration Ltd | Information & communication | 2017 |
| MTM Financial Services Limited | Professional & scientific | 2014 |
| Mudalla Technology Limited | Extraterritorial | 2018 |
| Murana Project Services Ltd | Information & communication | 2018 |
| Murrell Green Management Limited | Households | 1989 |
| Music Outreach Group CIC | Education | 2023 |
| Mustard Foods Limited | Manufacturing | 2008 |
| MVH Design House Ltd | Professional & scientific | 2013 |
| MWH Technology Services Limited | Information & communication | 2004 |
| Mwhps Limited | Information & communication | 2021 |
| Mwhr Limited | Information & communication | 2019 |
| Mxdr Ltd | Information & communication | 2022 |
| MXR Consulting Ltd | Professional & scientific | 2022 |
| My Little Planet Limited | Information & communication | 2004 |
| My PAD Haus Limited | Construction | 2013 |
| Myauto Limited | Extraterritorial | 2019 |
| Mynamechange Ltd | Financial services | 2010 |
| Mysa Essentials Ltd | Wholesale & retail | 2023 |
| Mystery Machine Limited | Information & communication | 2022 |
| Mytec Limited | Manufacturing | 1998 |
| Namika Sport Horses Ltd | Other services | 2017 |