| Maradean Limited | Real estate | 1992 |
| Maranis Limited | Professional & scientific | 2018 |
| March Consulting Limited | Other services | 2003 |
| March Hare Publishing Limited | Information & communication | 2003 |
| Marcian Limited | Professional & scientific | 2018 |
| Marcom (Marketing Communications) Ltd | Professional & scientific | 2002 |
| Marcus Andreen Limited | Professional & scientific | 2017 |
| Marcus Hawkins Limited | Professional & scientific | 2012 |
| MARIO7 Ltd | Health & social care | 2019 |
| Mark Bury Limited | Real estate | 2026 |
| Mark Evitts Limited | Professional & scientific | 2025 |
| Mark Flint Properties Limited | Real estate | 2026 |
| Mark Gilbert Builders Limited | Construction | 2007 |
| Mark Gunning After School and Holiday Care Ltd | Health & social care | 2021 |
| Mark Gunning Educational Consultancy Ltd | Education | 2021 |
| Mark Henden Electrical Limited | Construction | 2013 |
| Mark M. Coombs & Associates Limited | Information & communication | 2017 |
| Mark Millar Productions Ltd. | Information & communication | 2010 |
| Mark N Bijok Limited | Professional & scientific | 2000 |
| Mark Nash Limited | Construction | 2002 |
| Mark Pearson Renovation and Build Ltd | Construction | 2017 |
| Mark Raiss Consulting Ltd | Professional & scientific | 2024 |
| Mark Rogers Limited | Construction | 2005 |
| Mark Steeds Limited | Arts & recreation | 2004 |
| Mark Wray Architects Limited | Professional & scientific | 2013 |
| Marketforce (U.K.) Limited | Extraterritorial | 1951 |
| Marketing Consultancy (UK) Limited | Professional & scientific | 2011 |
| Marketmine Limited | Information & communication | 2006 |
| Marksbury Services Limited | Professional & scientific | 2025 |
| Markus Electrical Limited | Construction | 2013 |
| Marlborough Buildings (Bath) Limited | Households | 1983 |
| Marlborough Street Ltd | Real estate | 2024 |
| Marlborough Tavern Ltd | Hospitality | 2023 |
| Marlyns Drive Ltd | Professional & scientific | 2015 |
| Marmalade Enterprises Limited | Wholesale & retail | 2025 |
| Maronglow Limited | Professional & scientific | 1997 |
| Maroon Food and Drink Limited | Wholesale & retail | 2023 |
| Marptree Design & Build Limited | Construction | 2014 |
| Marr House Management Company Limited | Households | 2017 |
| Marsh Jewellery Co. Limited | Wholesale & retail | 1978 |
| Marshalsea Hydraulics Limited | Manufacturing | 1930 |
| Marston Fields Limited | Construction | 2017 |
| Marta Kissi Ltd | Professional & scientific | 2017 |
| Martialflow Ltd | Information & communication | 2025 |
| Martin Blake Associates Limited | Professional & scientific | 2006 |
| Martin Daniel Bathrooms by Design Limited | Wholesale & retail | 2012 |
| Martlyn Limited | Professional & scientific | 2017 |
| Mary Mount Limited | Hospitality | 2022 |
| Mashman Ltd | Arts & recreation | 2023 |
| Mason & COE Ltd | Construction | 2025 |
| Masro Limited | Information & communication | 2013 |
| MAT Paints Ltd | Arts & recreation | 2026 |
| Matai Holdings Limited | Financial services | 2026 |
| Matatu Catering Ltd | Hospitality | 2025 |
| Matcha Thing Ltd | Wholesale & retail | 2025 |
| Matchbox Productions Limited | Information & communication | 2019 |
| Material Impact Limited | Professional & scientific | 2007 |
| Matford Construction Group Limited | Construction | 2022 |
| Matford Homes Limited | Construction | 2022 |
| Matha Investment Limited | Financial services | 2024 |
| Matheson Charles Ltd | Financial services | 2021 |
| Matilda Ruth Limited | Arts & recreation | 2025 |
| Matlock Bath FB Ltd | Hospitality | 2025 |
| Matrix Asset Venture Ltd | Real estate | 2025 |
| Matrix Fencing Systems Limited | Wholesale & retail | 2006 |
| Matt Evans Landscapes Limited | Professional & scientific | 2026 |
| Matt Milsom Engineering Services Ltd | Construction | 2015 |
| Matt Shepherd Physiotherapy Limited | Health & social care | 2019 |
| Matter-Npd Ltd | Other services | 2002 |
| Matthew Tomlin Creative Services Ltd | Professional & scientific | 2024 |
| Maureen Cross Settlement Trustees Limited | Financial services | 2023 |
| Maven Energy Services Limited | Professional & scientific | 2016 |
| MAX Color Ltd | Manufacturing | 2016 |
| MAX Urch Limited | Transport & logistics | 2012 |
| Maxco Financial Limited | Professional & scientific | 2013 |
| Maximising Capability Limited | Professional & scientific | 2003 |
| Maxiurban Property Management Limited | Professional & scientific | 1987 |
| Maxwell Comms Limited | Professional & scientific | 2013 |
| Maya Invest London LLP | | 2012 |
| Maybrick Garages Management Company Limited | Other services | 2014 |
| Mayd Studio Ltd | Professional & scientific | 2019 |
| Mayden House Limited | Information & communication | 2000 |
| Mayden Ventures Limited | Information & communication | 2022 |
| Mayfield Hughes Limited | Professional & scientific | 2024 |
| Maystar Developments Limited | Real estate | 2004 |
| Maytrails Limited | Hospitality | 1983 |
| Maywood Communications Ltd | Professional & scientific | 2024 |
| Mbga Developments Ltd | Construction | 2024 |
| Mbira Festival CIC | Administrative & support | 2026 |
| MC Coding Limited | Information & communication | 2014 |
| MC Publishing Limited | Information & communication | 2002 |
| Mcaarp Two Limited | Extraterritorial | 2008 |
| Mcandrew Development Limited | Construction | 2008 |
| MCC3 Limited | Information & communication | 2005 |
| Mccaffer Limited | Construction | 2026 |
| Mcculloch Homes ( Sussex) Limited | Real estate | 2022 |
| Mcculloch Homes Limited | Construction | 1996 |
| Mcculloch New Homes Limited | Real estate | 2016 |
| Mccullochs ( Kent ) Limited | Real estate | 2024 |
| Mccullochs ( Orpington ) Limited | Real estate | 2019 |