| Marlowe Yard Limited | Professional & scientific | 1999 |
| Marmaduke Marketing Ltd | Administrative & support | 2015 |
| Marmalade Merchandise Limited | Administrative & support | 2019 |
| Marnikir Ltd | Transport & logistics | 2023 |
| Marourde Limited | Manufacturing | 2017 |
| Marriner Electrical Services Ltd | Construction | 2017 |
| Marshalls Mechanical Limited | Construction | 2010 |
| Marsisi Properties Limited | Real estate | 2022 |
| Mart (Developments) Limited | Real estate | 1977 |
| Martello Lakes Management Company Limited | Real estate | 2016 |
| Martin Hi-Tech Contracts Limited | Wholesale & retail | 1979 |
| Martin Nenchev Limited | Transport & logistics | 2016 |
| Martin Sexton Services Limited | Wholesale & retail | 2015 |
| Martin Vaughan Casting Ltd | Administrative & support | 2024 |
| Martin Wright Crown & Bridge Specialist Limited | Health & social care | 2015 |
| Martine Waghorn Consulting Limited | Real estate | 2003 |
| Martinks Tattoos Ltd | Other services | 2024 |
| Martins Holdings (2011) Limited | Other services | 2011 |
| Martins Upholstery Supplies Limited | Wholesale & retail | 1999 |
| Marvel Property Services Ltd | Construction | 2015 |
| Marwa Hayat Limited | Wholesale & retail | 2026 |
| Marwah Group Limited | Financial services | 2022 |
| Marwari Consulting Ltd | Real estate | 2023 |
| Mary Services Ltd | Administrative & support | 2019 |
| Mary-Ann Carino Ltd | Health & social care | 2012 |
| Mary-Anne Care Services Ltd | Health & social care | 2017 |
| MAS PAN Ltd | Information & communication | 2018 |
| Masaffeys Limited | Hospitality | 2026 |
| Masey's Jewellers (Tenterden) Limited | Wholesale & retail | 2016 |
| Masey's Jewellers Ltd | Wholesale & retail | 2011 |
| Masking Solutions Ltd | Wholesale & retail | 2025 |
| Masoj Solution Services UK Limited | Administrative & support | 2015 |
| Masolewy Limited | Arts & recreation | 2019 |
| Mason's Holdings Ltd | Wholesale & retail | 2017 |
| Massimiliano Ercolini Ltd | Administrative & support | 2010 |
| Master Craft Roofing Specialist Ltd | Construction | 2025 |
| Masters Contractors Ltd | Construction | 2025 |
| Masters of Dance Limited | Arts & recreation | 2014 |
| Matam Ltd | Financial services | 2022 |
| Match Point Challenge Limited | Information & communication | 2026 |
| Matchbox Motion Productions Limited | Information & communication | 2016 |
| Matchday Passport Ltd | Administrative & support | 2026 |
| Matchless Safety Limited | Professional & scientific | 2020 |
| Matco International UK Ltd | Wholesale & retail | 2023 |
| Matelix Ltd | Transport & logistics | 2024 |
| Mathaley Holdings Limited | Financial services | 2018 |
| Mathew Enterprises Limited | Health & social care | 2018 |
| Matmus Ltd | Wholesale & retail | 2021 |
| Matrix Farming Ltd | Wholesale & retail | 2020 |
| Matsbond Limited | Construction | 1976 |
| Matt Supply Ltd | Other services | 2017 |
| Mattdoesfitness Limited | Education | 2018 |
| Matthew Calver Limited | Wholesale & retail | 2006 |
| Matthew Harvey Holdings Limited | Real estate | 2021 |
| Matthews Ortho Ltd | Health & social care | 2023 |
| Matttrottphotography Limited | Professional & scientific | 2017 |
| Maty Trans Ltd | Transport & logistics | 2024 |
| Mavalon Limited | Information & communication | 2002 |
| Mavericks Marketing Ltd | Professional & scientific | 2023 |
| Mavin Care Ltd | Health & social care | 2022 |
| Mavridou Ltd | Health & social care | 2022 |
| MAX Cuisine Ltd | Hospitality | 2023 |
| MAX Gooding Ltd | Professional & scientific | 2022 |
| MAX Performance Ltd | Wholesale & retail | 2025 |
| MAX Zorin Industries Limited | Real estate | 2024 |
| Maximilian Oliver Limited | Administrative & support | 2026 |
| Maximus One Ltd | Real estate | 2020 |
| Maximus Trans Ltd | Transport & logistics | 2025 |
| Maxmilane Trading Ltd | Wholesale & retail | 2026 |
| Maxspeed Limited | Wholesale & retail | 2017 |
| Maxted Holdings Limited | Financial services | 2024 |
| Maxul Ltd | Real estate | 2020 |
| Maxxmora Ltd | Manufacturing | 2022 |
| Maya London Luxury Ltd | Wholesale & retail | 2025 |
| MAYA24FILM Ltd | Information & communication | 2018 |
| Mayair UK Holdings Limited | Financial services | 2024 |
| Maybugs Ltd | Wholesale & retail | 2021 |
| Mayday Properties Limited | Real estate | 2018 |
| Mayfair Capital Residential 2 LLP | | 2016 |
| Mayfair Global Trade Group Limited | Wholesale & retail | 2016 |
| Mayfair Insurance and Mortgage Consultants Limited | Financial services | 1988 |
| Mayfairex Limited | Professional & scientific | 2015 |
| Mayhem Solutions Limited | Extraterritorial | 1999 |
| Maylam Financial Planning Ltd | Administrative & support | 2017 |
| Maylams Quay Freehold Limited | Households | 2006 |
| Maylams Quay Management Limited | Households | 2005 |
| Maynard Meadows Management Co. Ltd | Households | 2022 |
| Mayo Ecommerce Ltd | Wholesale & retail | 2021 |
| Maypark Solutions Limited | Wholesale & retail | 2021 |
| Maytech Holdings Limited | Information & communication | 2018 |
| Maytree Management Co. Ltd | Households | 2023 |
| Mazda Hood Shop Limited | Administrative & support | 2010 |
| Maze Couture Limited | Real estate | 2023 |
| Mazel Ltd | Real estate | 2024 |
| MB Grounds Maintenance Limited | Administrative & support | 2017 |
| Mb&H Services Ltd | Wholesale & retail | 2026 |
| Mbarontransport Limited | Transport & logistics | 2017 |
| MBC Mobile Car Valeting Ltd | Administrative & support | 2025 |
| Mbien Consultants Limited | Other services | 2012 |
| Mbpc (Kent) Limited | Real estate | 2022 |