| Markin Instruments Limited | Professional & scientific | 2021 |
| Markland Estates Ltd | Real estate | 2024 |
| Marlands Opco Limited | Real estate | 2023 |
| Marlands Propco Limited | Financial services | 2023 |
| Marlborough Court (Bournemouth) Freehold Limited | Households | 1999 |
| Marlborough Court (Bournemouth) Management Company Limited | Households | 1961 |
| Marlborough Pines Freehold Limited | Households | 2013 |
| Marlowe Media Limited | Real estate | 2006 |
| Marna Holdings Ltd | Administrative & support | 2025 |
| Maroni Limited | Wholesale & retail | 2023 |
| Marotix Ltd | Wholesale & retail | 2025 |
| Marr's Electrical Limited | Construction | 2009 |
| Marrakech Cambridge Ltd | Hospitality | 2019 |
| Married to the MOP Ltd | Administrative & support | 2019 |
| Marrufo Consultancy Limited | Professional & scientific | 2015 |
| Mars 1982 Ltd | Information & communication | 2016 |
| Marsden Flooring Limited | Wholesale & retail | 2010 |
| Marshall Total Autos Limited | Wholesale & retail | 2026 |
| Marshes END Management Company Limited | Real estate | 1988 |
| Marson Projects Limited | Real estate | 2023 |
| Marston Court Management Company Limited | Households | 1996 |
| Mart Property Group Ltd | Construction | 2017 |
| Marte XP Ltd | Information & communication | 2025 |
| Martello House Property Limited | Households | 1982 |
| Martha's Walls Limited | Wholesale & retail | 2024 |
| Martin Marcin Nieweglowski Ltd | Information & communication | 2013 |
| Martin Petersen Ltd | Extraterritorial | 2025 |
| Martin Scott Ltd | Manufacturing | 2015 |
| Martin Simon Properties Limited | Real estate | 2012 |
| Martinas Engineering Solutions Ltd | Professional & scientific | 2025 |
| Martingales Limited | Professional & scientific | 2005 |
| Martlaz Limited | Wholesale & retail | 2025 |
| Marv.App Limited | Information & communication | 2019 |
| Marvelhd Ltd | Construction | 2025 |
| Maryam Alzaabi Limited | Wholesale & retail | 2025 |
| Maryams Market Ltd | Wholesale & retail | 2025 |
| MAS Design Products Limited | Professional & scientific | 2002 |
| Mascott Developments Ltd | Construction | 2015 |
| Maskvale Property Management Limited | Households | 1983 |
| Masma Limited | Construction | 2002 |
| Mason Inc Ltd | Wholesale & retail | 2024 |
| Mason Jones Solutions Ltd | Financial services | 2015 |
| Mass Extinction Monitoring Observatory | Education | 2007 |
| Mass Foam Systems Limited | Construction | 2014 |
| Massey Developments Limited | Financial services | 2017 |
| Massey Properties Limited | Real estate | 2020 |
| Massmend Limited | Professional & scientific | 2007 |
| Massoud Trading Limited | Wholesale & retail | 2025 |
| Master Class Hairdresser Ltd | Wholesale & retail | 2021 |
| Masterclass Scaffolding Ltd | Construction | 2022 |
| Mastermind Groups Global Ltd | Professional & scientific | 2024 |
| Masters GAS & Heating Ltd | Construction | 2025 |
| Masters of Dragons Ltd | Administrative & support | 2026 |
| Masters of Mayfair Limited | Wholesale & retail | 2013 |
| Masud Hasan Azzz Ltd | Wholesale & retail | 2025 |
| Mataatua Limited | Professional & scientific | 2021 |
| Match Homes Ltd | Real estate | 2006 |
| Match Recruitment Consultancy Limited | Administrative & support | 2015 |
| Match Wealth Management Ltd | Professional & scientific | 2011 |
| Matchbox Marketing Limited | Professional & scientific | 2015 |
| Matchday Locker Ltd | Wholesale & retail | 2025 |
| Matchdeckmedia Limited | Administrative & support | 2023 |
| Matchfit Football Limited | Arts & recreation | 2016 |
| Matevitality Ltd | Wholesale & retail | 2025 |
| Mathmos Limited | Manufacturing | 1990 |
| Maths Engine Ltd | Information & communication | 2015 |
| Maths Teaching Solutions Ltd | Professional & scientific | 2020 |
| Matilda Nicholls Ltd | Arts & recreation | 2025 |
| Matquel Property Co. Limited | Real estate | 1960 |
| Matred Limited | Construction | 2003 |
| Matt Monfredi Ltd | Professional & scientific | 2018 |
| Mattadaw Limited | Professional & scientific | 2017 |
| Matthews and Carter Associates Ltd | Administrative & support | 2016 |
| Matthews Creative Limited | Information & communication | 2022 |
| Mattrans WB Ltd | Transport & logistics | 2025 |
| Matvale Investments Ltd | Real estate | 2023 |
| Mauntley House Limited | Real estate | 2024 |
| Maura Properties Ltd | Real estate | 2023 |
| Maurer Holdings Limited | Real estate | 2025 |
| Mavenalysis Ltd | Administrative & support | 2017 |
| Mavenry Ventures Limited | Financial services | 2026 |
| Maverick Industries Limited | Construction | 2007 |
| Maverick Omega Limited | Manufacturing | 2020 |
| Maverick Skateparks Limited | Arts & recreation | 2008 |
| Mavrosoft Ltd | Information & communication | 2025 |
| MAW Education Ltd | Wholesale & retail | 2023 |
| MAX Body Ltd. | Wholesale & retail | 2020 |
| MAX Faction Limited | Wholesale & retail | 2020 |
| MAX Intermediações Limited | Wholesale & retail | 2025 |
| MAX Plan 2 Limited | Other services | 2016 |
| Maxamar Limited | Administrative & support | 2021 |
| Maximar Trading Ltd | Wholesale & retail | 2024 |
| Maximum Garage Doors Limited | Construction | 2024 |
| Maximus Roofing and Build Ltd | Administrative & support | 2023 |
| Maxomi Ltd | Financial services | 2018 |
| Maxwell Developments Limited | Real estate | 2019 |
| Maxwell Energy Ltd | Administrative & support | 2009 |
| Maya MAX 2024 Ltd. | Transport & logistics | 2025 |
| Maybu.Online Ltd | Extraterritorial | 2019 |
| Mayfair Goods Ltd | Wholesale & retail | 2025 |