| Marco Food Ltd | Hospitality | 2019 |
| Marco Studio Ltd | Administrative & support | 2024 |
| Marcus C Nolan Limited | Information & communication | 2025 |
| Marcus Young Environmental Services Ltd | Water & waste | 2009 |
| Mardell Healthcare Ltd | Health & social care | 2024 |
| Marell Drylining Ltd | Construction | 2023 |
| Marezi Group Ltd | Wholesale & retail | 2025 |
| Marfik Ltd | Wholesale & retail | 2025 |
| Marfleet Radiology Solutions Ltd | Professional & scientific | 2025 |
| Marford Developments Ltd | Construction | 2024 |
| Marford Homes Ltd | Construction | 2023 |
| Margaret Holding Ltd | Financial services | 2021 |
| Margaretbanhire Limited | Health & social care | 2013 |
| Margaux Developments Limited | Construction | 1996 |
| Marha EMP Ltd | Administrative & support | 2024 |
| Marhabar Ltd | Hospitality | 2021 |
| Maria Beautician II Limited | Other services | 2025 |
| Maria Beautician Limited | Wholesale & retail | 2025 |
| Maria Unisex Haircut Specialist Limited | Other services | 2025 |
| Maria's Domestic Cleaning Ltd | Administrative & support | 2024 |
| Marian & IM Ltd | Construction | 2021 |
| Marian Care Limited | Health & social care | 2014 |
| Marianaanani Limited | Health & social care | 2016 |
| Marianne Holt Limited | Real estate | 2018 |
| Marina HUT Ltd | Hospitality | 2019 |
| Marina Valets MK Ltd | Real estate | 2024 |
| Marine Marketing International Limited | Manufacturing | 1994 |
| Marino Properties Limited | Extraterritorial | 2001 |
| Mario Welder Limited | Manufacturing | 2019 |
| Marisa KOI Farm Limited | Agriculture & fishing | 2016 |
| Marisco & Torta Ltd. | Hospitality | 2020 |
| Marissa Property Ltd | Real estate | 2019 |
| Marius Muzic Limited | Transport & logistics | 2016 |
| Marius Sercau Ltd | Transport & logistics | 2024 |
| Marjaz Healthcare Ltd | Health & social care | 2023 |
| Mark a Wood Ltd | Professional & scientific | 2016 |
| Mark Beard Limited | Transport & logistics | 2019 |
| Mark Education PVT Ltd | Education | 2022 |
| Mark Goodridge Limited | Professional & scientific | 2011 |
| Mark Hammett Premier Equestrian Sales Limited | Wholesale & retail | 2026 |
| Mark I'Anson Property Limited | Real estate | 2009 |
| Mark Interiors Ltd | Construction | 2021 |
| Mark James Limited | Wholesale & retail | 2000 |
| Mark Robins Limited | Wholesale & retail | 2019 |
| Mark Rowntree Cabinet Maker Limited | Manufacturing | 2015 |
| Mark Scissors Barbers Ltd | Other services | 2026 |
| Marketcrew Ltd | Information & communication | 2025 |
| Marketing Powerhouse Limited | Professional & scientific | 1991 |
| MARKETPLACE4YOU Ltd | Wholesale & retail | 2025 |
| Markham Bespoke Furniture Limited | Manufacturing | 2022 |
| Markins Ltd | Wholesale & retail | 2023 |
| Marko Property Ltd | Construction | 2023 |
| Markstream Limited | Professional & scientific | 2000 |
| Markus Huber Enterprises Limited | Financial services | 2016 |
| Marla Dental Clinic Ltd | Health & social care | 2024 |
| Marlborough House Investment Holdings Limited | Real estate | 1988 |
| Marlespain Limited | Hospitality | 2014 |
| Marlin Motor Engineers Limited | Wholesale & retail | 2003 |
| Marlow Mortgages & Protection Ltd | Financial services | 2021 |
| Marlowe Green Developments Ltd | Construction | 2022 |
| Marmon Foodservice Technologies UK Limited | Manufacturing | 1947 |
| Marmura Limited | Construction | 2025 |
| Maroma Charters Limited | Transport & logistics | 2014 |
| Maron Auto Care Ltd | Wholesale & retail | 2021 |
| Marquee Chameleon Limited | Professional & scientific | 2020 |
| Married With Toys Limited | Wholesale & retail | 2014 |
| Marryoush Ltd | Transport & logistics | 2026 |
| Mars Accountants Ltd | Professional & scientific | 2017 |
| Mars Corps Limited | Professional & scientific | 2023 |
| Marsh (Rushey Mead) (NO.2) Management Company Limited | Households | 1992 |
| Marshall Accountancy & Training Services Limited | Professional & scientific | 2013 |
| Marshall Commercial Vehicles Limited | Extraterritorial | 1991 |
| Marshall Drive Residents Association Limited | Households | 1979 |
| Marshall Motor Group Limited | Wholesale & retail | 1934 |
| Marshall Motor Group Properties Limited | Real estate | 1986 |
| Marshall Motor Holdings Limited | Professional & scientific | 1986 |
| Marshall North West Limited | Wholesale & retail | 1937 |
| Marshall of Ipswich Limited | Wholesale & retail | 2002 |
| Marshall of Peterborough Limited | Wholesale & retail | 2003 |
| Marshall of Scunthorpe Limited | Wholesale & retail | 1974 |
| Marshall of Stevenage Limited | Wholesale & retail | 2007 |
| Marshall Oliver Limited | Administrative & support | 2010 |
| Marshall Plumbing and Heating Limited | Construction | 2017 |
| Marshall Records Limited | Information & communication | 2016 |
| Marshall Records Publishing Limited | Information & communication | 2017 |
| Marshall Shopfitters Limited | Construction | 2007 |
| Marsmap Ltd | Other services | 2024 |
| Marstek Optic-Computer & Communication International GmbH | | 1990 |
| Marston Fields (Property Management) Company NO.4 Limited | Administrative & support | 2005 |
| Martavia Engineering Ltd | Manufacturing | 2014 |
| Martelozzo Construction Ltd | Construction | 2019 |
| Martha Beyond Company Limited | Other services | 2024 |
| Marthaartha Limited | Education | 2023 |
| Martial Arts Networks Ltd | Information & communication | 2002 |
| Martigo Retail Limited | Wholesale & retail | 2025 |
| Martin & Maidment Property Ltd | Real estate | 2019 |
| Martin Cowling Architect Ltd | Administrative & support | 2019 |
| Martin GEE Limited | Professional & scientific | 1998 |
| Martin Homes Burgess Hill Ltd | Real estate | 2019 |
| Martin Homes Wivelsfield Ltd | Real estate | 2019 |