| Martec Business Systems Limited | Manufacturing | 1998 |
| Martello View (Hastings Avenue) RTM Company Limited | Households | 2004 |
| Martelly Group Ltd. | Water & waste | 2022 |
| Martial Arts Intelligence Ltd | Education | 2022 |
| Martin Contractors London Ltd | Construction | 2014 |
| Martin Reddington Associates Limited | Professional & scientific | 2014 |
| Martins Santos Limited | Construction | 2019 |
| Martins Wine Merchants Limited | | 1956 |
| Martscorp Ltd | Real estate | 2022 |
| Mary Regina Care Homes Limited | Health & social care | 2023 |
| Mary's Terrace Limited | Manufacturing | 2013 |
| Marzano CFO Advisory Ltd | Professional & scientific | 2026 |
| Marzano Properties Limited | Real estate | 2022 |
| Mashaallah Mobile Limited | Wholesale & retail | 2020 |
| Masiur Propery Limited | Real estate | 2026 |
| Masonic Construction and Landscapes Ltd | Construction | 2018 |
| Masons Bridge Ltd | Wholesale & retail | 2025 |
| Mass Observation Ltd | Wholesale & retail | 2020 |
| Mass Tints Bromley Ltd | Manufacturing | 2025 |
| Massogo Limited | Wholesale & retail | 2021 |
| Master Co-Creators Ltd | Information & communication | 2025 |
| Master Plus Linguistics Ltd | Administrative & support | 2017 |
| Mastermind Developments Ltd | Construction | 2022 |
| Mastery Services Limited | Education | 2021 |
| Matador Kebab Limited | Hospitality | 2024 |
| Matbrick Properties Maintenance Limited | Households | 1964 |
| Mathzoo Ltd | Information & communication | 2025 |
| Matipa Ltd | Professional & scientific | 2016 |
| Matiss Ltd | Information & communication | 2019 |
| Matriarch Homes UK Ltd | Health & social care | 2019 |
| Matt Build Ltd | Construction | 2018 |
| Matt Clayton Photography Limited | Professional & scientific | 2013 |
| Matt Hope Limited | Manufacturing | 2018 |
| Matthew Cava Limited | Information & communication | 2006 |
| Matthew Gonzalez Ltd | Manufacturing | 2020 |
| Mattison & Co Accountants Limited | Professional & scientific | 2022 |
| Mave Properties Limited | Real estate | 2019 |
| Maverick Warnes Limited | Financial services | 2024 |
| MAX AI Trading Ltd | Information & communication | 2024 |
| MAX and Avery Ltd | Hospitality | 2025 |
| MAX Golf Ltd | Arts & recreation | 2020 |
| Maxim Marketing and Management Services Limited | Administrative & support | 2015 |
| Maximum Impact Limited | Professional & scientific | 2013 |
| Maxinames Ltd | Wholesale & retail | 2022 |
| Maxwell Kusi Limited | Transport & logistics | 2015 |
| Maxwell Security Solutions Limited | Administrative & support | 2022 |
| Maycode Limited | Financial services | 2017 |
| Mayday Films Limited | Information & communication | 2009 |
| Mayfield House Freehold Limited | Households | 1996 |
| Mayfield House Residents Limited | Households | 2007 |
| Mayfields (Blackheath) Management Company Limited | Households | 1986 |
| Maygate Limited | Manufacturing | 1958 |
| Mayn Finance Limited | Professional & scientific | 2026 |
| Mayne (Consultants Services) Limited | Construction | 2015 |
| Mayne Property Holdings Limited | Real estate | 2021 |
| Mayne Technical Services Ltd | Construction | 2023 |
| Mayon Consultancy Limited | Information & communication | 2007 |
| Mayoo Limited | Wholesale & retail | 2018 |
| Mayukha Property Ltd | Real estate | 2021 |
| MB Built Environment Ltd | Professional & scientific | 2026 |
| Mbaise Limited | Real estate | 2026 |
| MBC Retail Consulting Limited | Administrative & support | 2006 |
| Mblb Properties Limited | Real estate | 2024 |
| Mbmp Limited | Manufacturing | 2020 |
| MCB Prolific Property Investment Ltd | Real estate | 2023 |
| Mccarron Architects Ltd | Professional & scientific | 2023 |
| Mccoda (Holdings) Ltd | Financial services | 2020 |
| Mccoda Ltd | Construction | 2013 |
| Mccolloch Roofing Ltd | Construction | 2015 |
| Mcdb Software Limited | Information & communication | 2024 |
| Mcdonnell Psychology Ltd | Administrative & support | 2020 |
| Mcguinn Electrical Limited | Energy | 2013 |
| Mcjoe Care Support Limited | Health & social care | 2026 |
| Mckenna Demolition (South East) Limited | Construction | 2011 |
| Mckenna Holdings Limited | Financial services | 1998 |
| MCL Industry Ltd | Extraterritorial | 2014 |
| MCL Property Management Limited | Real estate | 2021 |
| Mcleod Tile Restoration Limited | Construction | 2012 |
| Mcmahon & Karoo Associates Ltd | Real estate | 2017 |
| Mcmlx Ltd | Administrative & support | 2019 |
| Mcmullan Page Limited | Other services | 2024 |
| Mcom Insights Limited | Information & communication | 2013 |
| MCQ Global Ltd | Professional & scientific | 2025 |
| Mcqueen Clean Limited | Administrative & support | 2009 |
| Mcqueens Solicitors LLP | | 2015 |
| MD & G Services Limited | Transport & logistics | 2023 |
| MD Disposal Ltd | Transport & logistics | 2022 |
| MD Sagor Limited | Transport & logistics | 2024 |
| MDM Aberdeen Union Limited | Hospitality | 2025 |
| MDM Glenrothes Limited | Hospitality | 2025 |
| MDM Group Enterprises Ltd | Financial services | 2025 |
| MDM ST Andrews Limited | Hospitality | 2026 |
| ME and YOU Create Limited | Extraterritorial | 2019 |
| ME Holiday Homes Ltd | Hospitality | 2026 |
| ME Print Limited | Manufacturing | 2019 |
| Meadow Heights Properties Limited | Real estate | 2019 |
| Meadowcroft Lodge Ltd | Construction | 1986 |
| Meadowview Business Centres Limited | Real estate | 1993 |
| Meadowview Estate Company Limited | Real estate | 2001 |
| Meads Court (London) RTM Company Limited | Real estate | 2021 |