| Marsango & Sons Properties Limited | Real estate | 2002 |
| Marsden House Limited | Real estate | 2003 |
| Marsden House RTM Company Ltd | Households | 2025 |
| Marshall Flight Refinishing Limited | Transport & logistics | 2010 |
| Marshalls Scaffolding Ltd | Construction | 2026 |
| Marshals Accountants Limited | Professional & scientific | 1997 |
| Marshals Ltd | Administrative & support | 2017 |
| Marshalsea Consulting Limited | Information & communication | 2014 |
| Marshclass Limited | Information & communication | 1996 |
| Marshels Dorset Limited | Real estate | 2017 |
| Marski Ltd | Professional & scientific | 2022 |
| Marta Ltd | Extraterritorial | 2020 |
| Martell Mailing Limited | Transport & logistics | 2004 |
| Martial Arts & Fitness Club | Arts & recreation | 2019 |
| Martin & Co. (U.K.) Limited | Real estate | 1994 |
| Martin & Green Properties Ltd | Real estate | 2023 |
| Martin Bebbington Limited | Construction | 2009 |
| Martin E. Rabbets Limited | Administrative & support | 2004 |
| Martin Investments Ltd | Real estate | 2023 |
| Martin Professional Carpentry and Joinery Limited | Construction | 2019 |
| Martin Scott Holdings Limited | Real estate | 2021 |
| Marval-Mortimer Associates Ltd | Real estate | 2026 |
| Mary Beauty Clinic Ltd | Other services | 2025 |
| Mary Bowes Terrace Management Company Ltd | Households | 2022 |
| Marya Global UK Limited | Wholesale & retail | 2024 |
| Maryjanesplace Limited | Wholesale & retail | 2026 |
| Marywharf Limited | Real estate | 2021 |
| MAS Brothers Ltd | Hospitality | 2025 |
| Mascot Bespoke Homes Limited | Construction | 2008 |
| Maseko International Ltd | Information & communication | 2021 |
| Mason & Co Property Consultants Limited | Real estate | 2019 |
| Mason's Clean Co Ltd | Administrative & support | 2026 |
| Massage Merit Spa Ltd | Other services | 2023 |
| Massimo Barbato Ltd | Information & communication | 2025 |
| Massive Elege Ltd | Education | 2020 |
| Massive Maker Ltd. | Information & communication | 2016 |
| Massudd Limited | Hospitality | 2019 |
| Mast-Rig-Uk Services Limited | Information & communication | 2007 |
| Master Brazil Limited | Hospitality | 2023 |
| Master Cleaning Group Ltd | Administrative & support | 2015 |
| Master Cleaning Lettings Ltd | Administrative & support | 2018 |
| Master Tradesman Ductwork Solutions Limited | Construction | 2016 |
| Masterclass Exteriors Ltd | Construction | 2026 |
| MASTERKEBAB142 Ltd | Hospitality | 2025 |
| Masters Court RTM Company Limited | Households | 2025 |
| Masters Marketing & Management International Ltd | Real estate | 2022 |
| Masterson Breen Ltd | Health & social care | 2026 |
| Masto Property Ltd | Real estate | 2024 |
| Matacro Services Ltd | Information & communication | 2013 |
| Matchams Manor Farm Limited | Hospitality | 1999 |
| Matchams Manor Management Limited | Hospitality | 1993 |
| Matchbox Trading Limited | Wholesale & retail | 2017 |
| Matchedwise Ltd | Education | 2025 |
| MATEO2025 Ltd | Wholesale & retail | 2025 |
| Mathaai Ltd | Hospitality | 2025 |
| Mathew’S Taproom Ltd | Hospitality | 2026 |
| Matrix Construction (South) Limited | Construction | 2008 |
| Matt Joel Group Ltd | Hospitality | 2026 |
| Matt Precision Coach Ltd | Health & social care | 2025 |
| Matteo Rowland Limited | Wholesale & retail | 2022 |
| Matteolocumrx Limited | Professional & scientific | 2017 |
| Matteu Ltd | Arts & recreation | 2023 |
| Matthew & Matthew Limited | Professional & scientific | 2009 |
| Matthew Clarke Chiropractic Ltd | Health & social care | 2025 |
| Matthew Seare Motors Limited | Wholesale & retail | 2013 |
| Matthew Wilkins Landscapes Ltd | Administrative & support | 2014 |
| Matthew Winchester Ltd | Professional & scientific | 2014 |
| MATTHEWS724 Ltd | Real estate | 2022 |
| Matwin Management Services Ltd | Professional & scientific | 2007 |
| Maura Rewers Ltd | Hospitality | 2017 |
| Mauromal Limited | Administrative & support | 2020 |
| Maverick 7 Investments Limited | Real estate | 2018 |
| Mavic House Ltd | Professional & scientific | 2024 |
| Mavis Shoes Limited | Wholesale & retail | 2018 |
| Mavronlar Limited | Real estate | 2025 |
| MAW Corporation Limited | Administrative & support | 2017 |
| MAW Healthcare Limited | Health & social care | 2015 |
| MAX Level Ltd | Construction | 2026 |
| MAX Paris Kitchen Services Limited | Manufacturing | 2018 |
| MAX Worsley Plumbing & Heating Ltd | Construction | 2015 |
| Maxbra Ltd | Wholesale & retail | 2022 |
| Maxi Investments Limited | Households | 2015 |
| Maxi Market Limited | Wholesale & retail | 2022 |
| Maxim Security Ltd | Administrative & support | 2019 |
| Maxims Restaurants Limited | | 1988 |
| Maxmgb Limited | Hospitality | 2026 |
| Maxtopia Systems Limited | Information & communication | 2024 |
| Maxwel MK Ltd | Administrative & support | 2015 |
| Maxxiclean Ltd | Administrative & support | 2019 |
| MAY Wigs Collection Ltd | Wholesale & retail | 2025 |
| Maya Specialist Limited | Construction | 2020 |
| Maycorp Limited | Professional & scientific | 2018 |
| Maynard Keynes Limited | Professional & scientific | 2008 |
| Mayrit Limited | Health & social care | 2020 |
| Maytree House Property Management Ltd | Households | 2009 |
| Mazz Kebab House Ltd | Hospitality | 2018 |
| MB04 Ltd | Wholesale & retail | 2024 |
| MBH Holdings Ltd | Professional & scientific | 2014 |
| Mbin Limited | Hospitality | 2020 |
| MBL Construction Services Limited | Construction | 2017 |