| Masons Stone & Home Repairs Ltd | Manufacturing | 2021 |
| Master Trade House Limited | Wholesale & retail | 2017 |
| Masti Masala Limited | Extraterritorial | 2022 |
| Mastin.Dfl Ltd | Other services | 2019 |
| Match Muse Limited | Hospitality | 2025 |
| Matchstick Venues Limited | Hospitality | 2023 |
| Matel 1 Ltd | Hospitality | 2024 |
| Mather Jamie (Holdings) Limited | Financial services | 2018 |
| Mathorp Investments Limited | Financial services | 2020 |
| Mathorp Limited | Real estate | 2016 |
| Matt Bergin Physiotherapy Ltd | Health & social care | 2024 |
| Matt Ward Coaching Ltd | Other services | 2025 |
| Matthew Walne Limited | Other services | 2012 |
| Matthews and Cook Ltd | Professional & scientific | 2023 |
| Matthews Performance Limited | Arts & recreation | 2022 |
| Matthews Studio Ltd | Information & communication | 2020 |
| Mattioli Fishings Ltd | Agriculture & fishing | 2025 |
| Mattioli Holdings Ltd | Financial services | 2025 |
| Maverick Hotels and Inns Limited | Hospitality | 2003 |
| Maverick Venue Management Limited | Hospitality | 2006 |
| Mavunkal PVT Ltd | Hospitality | 2025 |
| Mawddach Crab Limited | Real estate | 2020 |
| Maxibounce Limited | Manufacturing | 2000 |
| Maxin Foods Ltd | Hospitality | 2019 |
| Maxin Pizza and Chicken Ltd | Hospitality | 2021 |
| Maxoptra Limited | Professional & scientific | 2018 |
| MAY & MAY Ltd | Professional & scientific | 2016 |
| Maya Fashions Ltd | Manufacturing | 2024 |
| Mayes Academy Ltd | Arts & recreation | 2016 |
| Mayfair Wholesale Limited | Hospitality | 2024 |
| Maytree Care Limited | Health & social care | 2022 |
| MB Automotive Ltd | Wholesale & retail | 2010 |
| MB Performance Limited | Arts & recreation | 2020 |
| Mbks Investments Limited | Real estate | 2025 |
| Mcconnachie Holdings Limited | Extraterritorial | 2003 |
| Mccs Engineering Ltd | Professional & scientific | 2020 |
| Mcdale Group Trading Ltd | Wholesale & retail | 2018 |
| Mcglynn Properties Ltd | Real estate | 2019 |
| Mchugs UK Ltd | Wholesale & retail | 2025 |
| Mcinnes Capital Ltd | Financial services | 2026 |
| MCJ Energy Solutions Ltd | Wholesale & retail | 2024 |
| Mckay Electrical Contractors Ltd | Construction | 2025 |
| Mcmo Properties Ltd | Construction | 2026 |
| Mcpv Performance Limited | Arts & recreation | 2023 |
| MDA Technologies Limited | Other services | 2017 |
| Mdc(Yorkshire) Limited | Information & communication | 2022 |
| MDS Loughborough Ltd | Wholesale & retail | 2024 |
| ME & HIM Limited | Information & communication | 2007 |
| ME ME Hair and Beauty Limited | Other services | 2015 |
| Meade Heating Ltd | Construction | 2016 |
| Meadow Farm Holdings Limited | Arts & recreation | 2024 |
| Meadow Farm Marina Ltd | Arts & recreation | 1999 |
| Meadow's Animal Healthcare Limited | Wholesale & retail | 2002 |
| Meal IT Limited | Hospitality | 2025 |
| Meals 4U Limited | Information & communication | 2014 |
| Meanwood Training Camp Limited | Arts & recreation | 2025 |
| Mechanical Engineer Design Ltd | Professional & scientific | 2025 |
| Mechanical Engineering Services (Midlands) Ltd | Professional & scientific | 2016 |
| Mechatronics Labs Ltd | Professional & scientific | 2019 |
| MEDDOSE3D Ltd | Wholesale & retail | 2024 |
| Medex Medical Emea Limited | Health & social care | 2012 |
| Media Monkey (UK) Limited | Manufacturing | 2002 |
| Medsyndesign Limited | Professional & scientific | 2012 |
| Megasense Limited | Information & communication | 2026 |
| Megastrikers Ltd | Education | 2020 |
| Meghna Medical Ltd | Health & social care | 2023 |
| Mehma Bridgen Ltd | Professional & scientific | 2026 |
| Meid Projects Limited | Construction | 2019 |
| Meinsen Ltd | Information & communication | 2025 |
| Melbourne Homes Ltd | Real estate | 2026 |
| Mellish Engineering Services Limited | Manufacturing | 2021 |
| Mellor Catering Services Ltd | Hospitality | 2024 |
| Melrose Ground Care Ltd | Administrative & support | 2023 |
| Melton Leisure Services Limited | Hospitality | 1992 |
| Meltransport Ltd | Transport & logistics | 2023 |
| Membrance Ltd | Information & communication | 2019 |
| Memoria-Uk Ltd | Health & social care | 2023 |
| Memorial Wood Pet Crematorium Limited | Other services | 2015 |
| Memory Box App Limited | Information & communication | 2025 |
| Mendz Moves Limited | Manufacturing | 2013 |
| Mental Health Fitness UK Ltd | Education | 2020 |
| Merchant Mews Management Company Limited | Real estate | 1998 |
| Mercia Football Ltd | Arts & recreation | 2025 |
| Merin Holidays Limited | Administrative & support | 2019 |
| Merrin Sparrow Management Limited | Real estate | 2009 |
| Merv's Kitchen Limited | Hospitality | 2022 |
| Mesh Tech Consulting Ltd | Professional & scientific | 2014 |
| Meslek Sports Limited | Arts & recreation | 2025 |
| Mesothelioma UK Trading Ltd | Other services | 2020 |
| MET Project Solutions Limited | Extraterritorial | 2017 |
| Metaknowledge Limited | Information & communication | 2026 |
| Metaverse Property Limited | Real estate | 2021 |
| Meteora Consulting Ltd | Information & communication | 2016 |
| Metritech Ltd | Information & communication | 2024 |
| Metrix Accountancy Services Limited | Administrative & support | 2018 |
| Metrix Pension Services Limited | Administrative & support | 2018 |
| Meyers and Davey Limited | Agriculture & fishing | 1950 |
| MG Play Inspections Ltd | Public administration | 2022 |
| MG Toxicology Consulting Ltd | Health & social care | 2012 |
| MGR Retail Ltd | Wholesale & retail | 2011 |