| Marbeth Consulting Limited | Professional & scientific | 2000 |
| Marble UK (Warrington) Ltd | Construction | 2026 |
| Marc Morris Services Limited | Other services | 2015 |
| March Bidco Limited | Other services | 2024 |
| March Holdco Limited | Other services | 2024 |
| March Midco Limited | Other services | 2024 |
| March Surveying Services Ltd | Information & communication | 2017 |
| Marchcroft (Management Company) Limited | Real estate | 2012 |
| Marco Electrical Engineers Limited | Professional & scientific | 2017 |
| Marco Heating & Plumbing Services Limited | Construction | 2025 |
| Marcol Business Services Limited | Professional & scientific | 1998 |
| Marcot Ltd | Manufacturing | 2017 |
| Marcus Brook Limited | Hospitality | 1978 |
| Marcus Group Ltd | Administrative & support | 2019 |
| Mareric Limited | Health & social care | 2022 |
| Mares Consulting Ltd | Real estate | 2021 |
| Margot & Bear Ltd | Wholesale & retail | 2024 |
| Mari Medical Imaging Consultancy and Services Limited | Health & social care | 2010 |
| Maria Dean Ltd | Professional & scientific | 2012 |
| Marian Homes Limited | Real estate | 2017 |
| Mariella Balazs Ltd | Professional & scientific | 2025 |
| Marigold IT Ltd | Information & communication | 2019 |
| Marillo Foods Holdings Ltd | Financial services | 2023 |
| Marillo Foods Limited | Wholesale & retail | 2002 |
| Marillo Properties Holdings Ltd | Financial services | 2023 |
| Marillo Properties Ltd | Real estate | 2023 |
| Marina Media Limited | Professional & scientific | 2017 |
| Marinas Fish Bar Limited | Hospitality | 2025 |
| Marine Diesel Engineering Limited | Manufacturing | 2013 |
| Mario Laundry Services Ltd | Other services | 2015 |
| Maris Seafoods Limited | Wholesale & retail | 2014 |
| Marise Sera Ltd | Wholesale & retail | 2022 |
| Maritime Offshore Limited | Administrative & support | 2026 |
| Mariuta Trans Ltd | Transport & logistics | 2018 |
| Mark Bird Limited | Information & communication | 2017 |
| Mark Browning 2011 Limited | Administrative & support | 2011 |
| Mark Evans Transport (NW) Ltd | Transport & logistics | 2020 |
| Mark Green Services Ltd | Construction | 2019 |
| Mark Hardie Consultancy Ltd | Professional & scientific | 2020 |
| Mark IT Solutions Limited | Administrative & support | 2026 |
| Mark Kellett Ltd | Health & social care | 2017 |
| Mark Knight Design Services Limited | Administrative & support | 2010 |
| Mark Lane Estates Developments Ltd | Real estate | 2022 |
| Mark Lane Estates Rentals Limited | Real estate | 2025 |
| Mark Mcelvaney Instrument Services Ltd | Administrative & support | 2026 |
| Mark Owens Joinery Limited | Construction | 2006 |
| Mark Telecom Limited | Information & communication | 2016 |
| Mark Thompson Ltd | Professional & scientific | 2003 |
| Mark Thompson Transport Ltd | Transport & logistics | 2009 |
| Mark William Chapman Ltd | Extraterritorial | 2024 |
| Market-Ng Ltd | Professional & scientific | 2025 |
| Marketing LAB North West Ltd | Professional & scientific | 2012 |
| Marketing List Limited | Information & communication | 2006 |
| Marketing Lounge Limited | Information & communication | 2024 |
| Marketing Planning Services Limited | Administrative & support | 2014 |
| Marketing Results Limited | Administrative & support | 2000 |
| Markey Engineering Limited | Administrative & support | 2016 |
| Markitecture Limited | Professional & scientific | 2019 |
| Markstone Software Ltd | Information & communication | 2015 |
| Marley and Rosie Property Rentals Ltd | Real estate | 2022 |
| Marlor Techs Ltd | Administrative & support | 2026 |
| Marlow IT Consultants Ltd | Administrative & support | 2026 |
| Marlva Limited | Professional & scientific | 2025 |
| Marlèt Clothing Limited | Wholesale & retail | 2026 |
| Marpol Security Limited | Administrative & support | 1992 |
| Marquis & Dawe Limited | Wholesale & retail | 2012 |
| Marra Rail Limited | Professional & scientific | 2014 |
| Marriage Made in Heaven C.I.C. | Other services | 2024 |
| Marrs and Hewitt Limited | | 1985 |
| Marsan Engineering Ltd | Professional & scientific | 2007 |
| Marsh Risk Associates Limited | Professional & scientific | 2023 |
| Marshall Driver Hire Ltd | Transport & logistics | 2022 |
| Marshall Marketing Campaigns Limited | Professional & scientific | 2021 |
| Marshall Project Management & Consultancy Services Limited | Administrative & support | 2013 |
| Martell Civil Engineering Limited | Administrative & support | 2024 |
| Martha & Mathew Ltd | Health & social care | 2022 |
| Martin ASH Limited | Administrative & support | 2013 |
| Martin Blythe Casings Ltd | Manufacturing | 2007 |
| Martin Dawes Limited | Wholesale & retail | 2009 |
| Martin Dugdale Landscape Maintenance Limited | Administrative & support | 2013 |
| Martin Lonergan & Associates Ltd | Professional & scientific | 2018 |
| Martin Polak Ltd | Transport & logistics | 2018 |
| Martinda Limited | Information & communication | 2016 |
| Martins Quality Solutions Limited | Professional & scientific | 2017 |
| Martyn John Building Limited | Construction | 2011 |
| Martyskitchen Ltd | Hospitality | 2022 |
| Marutis Capital Limited | Real estate | 2024 |
| Marveledge Consulting Limited | Professional & scientific | 2025 |
| Marvics Tech UK Ltd | Information & communication | 2019 |
| Marvin Haulage Ltd | Transport & logistics | 2026 |
| Mary Murtagh Media Limited | Administrative & support | 2013 |
| Mary's Salon Ltd | Other services | 2024 |
| Marylebone Records Limited | Extraterritorial | 2020 |
| MAS Telecom Solutions Ltd | Professional & scientific | 2018 |
| Masc Futura Limited | Administrative & support | 2024 |
| Mash Chef Services Ltd | Hospitality | 2015 |
| Mason Installations Limited | Construction | 2010 |
| Mason Parker Ltd | Administrative & support | 2009 |
| Massalux Ltd | Wholesale & retail | 2025 |
| Masson Design Ltd | Professional & scientific | 2019 |