| Lycett Scaffolding Limited | Construction | 2005 |
| Lydon & Co Property Investments Ltd. | Construction | 2018 |
| M & B Electrical Services (Reading) Limited | Construction | 2003 |
| M D Julius Event Consultancy Limited | Professional & scientific | 2026 |
| M J Bryant Consultancy Services Ltd | Information & communication | 2007 |
| M J Hughes Coins Limited | Wholesale & retail | 2023 |
| M N B Designs Ltd | Construction | 2015 |
| M N B Horticulture Limited | Other services | 2017 |
| M N Mollon & Partners Limited | Professional & scientific | 2017 |
| M Southern Carpentry Ltd | Construction | 2021 |
| M&M Digital Services Limited | Information & communication | 2023 |
| M-W-Architectural Ltd | Agriculture & fishing | 2023 |
| M. D. a. UK Enterprises Limited | Construction | 2013 |
| M.E.S Roofing & Installation Services Limited | Construction | 2026 |
| M7 Planning Limited | Real estate | 2018 |
| M7 SW LLP | | 2020 |
| Maack Ltd | Construction | 2013 |
| Maack Property Ltd | Real estate | 2021 |
| Macallan Penfold Limited | Professional & scientific | 1999 |
| Macaroon Ltd | Professional & scientific | 2026 |
| Macroteach Limited | Education | 1999 |
| Magical Mystery BUS Limited | Information & communication | 2018 |
| Maidenhead (T) Hairdressing Limited | Other services | 2008 |
| Maidstone (T2) Hairdressing Limited | Other services | 2017 |
| Main Garden Services Ltd | Agriculture & fishing | 2003 |
| Mainline & Maritime Limited | Information & communication | 2011 |
| Mainly Black London Limited | Wholesale & retail | 2015 |
| Maison Fundu Limited | Real estate | 2024 |
| Majorom Digital Ltd | Professional & scientific | 2018 |
| Make Creative Marketing Limited | Administrative & support | 2013 |
| Make My Day Flowers Limited | Wholesale & retail | 2023 |
| Makeovers by Tauntons Limited | Construction | 2020 |
| Makinarium UK Ltd | Manufacturing | 2019 |
| Malbi Design Ltd | Financial services | 2009 |
| Maldwyn Estates Limited | Information & communication | 2022 |
| Mallard Estate Agents Limited | Real estate | 2025 |
| Mallory AP LLP | | 2026 |
| Manifesto Ltd | Education | 2024 |
| Manny's Coffee Limited | Hospitality | 2024 |
| Mantana LCP Limited | Other services | 2025 |
| Maple Building Services (Hampshire) Ltd | Construction | 2007 |
| Marbans Estates Ltd | Real estate | 2025 |
| Marina & Port Services Ltd | Construction | 1983 |
| Marina Technical Services Limited | Construction | 1989 |
| Marine Salt Limited | Professional & scientific | 2016 |
| Marketing Communication Services Limited | Professional & scientific | 2001 |
| Markham Plant Ltd | Wholesale & retail | 2024 |
| Marmalade Skies Designs Limited | Manufacturing | 2023 |
| Marram Properties LLP | | 2025 |
| Marshall Developments Limited | Construction | 2003 |
| Marshall Health & Wellbeing Limited | Health & social care | 2018 |
| Martin Cashmore Property Limited | Real estate | 2014 |
| Martin Cashmore Fencing Limited | Construction | 2008 |
| Martin Family Holdings Limited | Real estate | 2022 |
| Martin Roden Financial Services Limited | Administrative & support | 2003 |
| Martin Watts Ltd | Construction | 2012 |
| Mascolo & Styles Limited Liability Partnership | | 2003 |
| Mascolo (UK) Holdings Limited | Professional & scientific | 2007 |
| Mascolo Family Partnership Ltd | Real estate | 2011 |
| Mascolo Group Limited | Wholesale & retail | 1994 |
| Mascolo Holdings Limited | Professional & scientific | 2010 |
| Mascolo Limited | Other services | 1963 |
| Mascolo Styles Limited | Professional & scientific | 2021 |
| Matthew Curtis Holdings Ltd | Financial services | 2017 |
| Mattoc Confectionery Engineering Ltd | Manufacturing | 2020 |
| Maxis Media Ltd | Professional & scientific | 2024 |
| Maygate Place Limited | Households | 2022 |
| Mayilan Ltd | Administrative & support | 2025 |
| Mbhbars Limited | Wholesale & retail | 2019 |
| MC Salons (Chipping Campden) Limited | Other services | 2017 |
| MC8 Consultants Ltd | Administrative & support | 2008 |
| Mccaffery Construction Limited | Construction | 1999 |
| Mcgavin Investments Ltd | Real estate | 2022 |
| Mckenzie Brothers Limited | Agriculture & fishing | 2003 |
| Mckenzie Brothers LP | | 2023 |
| Mcneil Venue Holdings Limited | Financial services | 2022 |
| Mcneill Investments Limited | Wholesale & retail | 1988 |
| MDB Trading Ltd | Wholesale & retail | 2024 |
| Meavy Consulting Limited | Financial services | 2022 |
| Medano Limited | Professional & scientific | 2009 |
| Medes Property Development Ltd | Construction | 2024 |
| Media Geeks Ltd | Administrative & support | 2021 |
| Mediafetch Limited | Information & communication | 2005 |
| Medimaps Technologies Limited | Information & communication | 2017 |
| Medina Marina Limited | Construction | 1961 |
| Medstead Bowls Club Ltd | Arts & recreation | 2024 |
| Medstead Community Enterprises Ltd | Health & social care | 2017 |
| Melanie Farming Holdings Limited | Agriculture & fishing | 2005 |
| Melanie Jenkins Farming Limited | Agriculture & fishing | 2005 |
| Melanie Ward Ltd | Construction | 2018 |
| Memo Designs Ltd | Professional & scientific | 2024 |
| Memories Clothing Ltd | Wholesale & retail | 2021 |
| Mengusto UK Ltd | Wholesale & retail | 2025 |
| Merelis Limited | Professional & scientific | 2021 |
| Messenger and Sons Ltd | Construction | 2023 |
| Metal Conker Limited | Financial services | 2020 |
| Metaletch Limited | Manufacturing | 1983 |
| Metapixel Studio Ltd | Professional & scientific | 2015 |
| Metapixel World Limited | Arts & recreation | 2022 |
| Meteor Management Limited | Education | 2014 |