| Market Square Fish Bar Limited | Hospitality | 2015 |
| Marks Security Services Ltd | Administrative & support | 2023 |
| Marpell Properties Limited | Construction | 2014 |
| Marriott Machinery Limited | Manufacturing | 2013 |
| Mars Sameday Limited | Transport & logistics | 2020 |
| Marsh Smart Homes Ltd | Construction | 2025 |
| Martin J Davis Limited | Information & communication | 2006 |
| Martin Spittle Limited | Construction | 2006 |
| Martin Wheeler Limited | Construction | 2005 |
| Martini Moves Ltd | Transport & logistics | 2020 |
| Masara's Limited | Transport & logistics | 2022 |
| Masboro Lodge RTM Company Limited | Households | 2019 |
| Mascott Sports Ltd | Professional & scientific | 2013 |
| Massa Solutions Limited | Extraterritorial | 2003 |
| Master Pens Ltd | Construction | 2021 |
| Matchbridge Technology Ltd | Information & communication | 2024 |
| Matipe Ltd | Administrative & support | 2011 |
| Matt Norris Engineering Ltd | Manufacturing | 2013 |
| Mattlok Ltd | Health & social care | 2025 |
| Matts Farriery Limited | Agriculture & fishing | 2025 |
| Mauger Garage Services Ltd | Wholesale & retail | 2015 |
| Maugers Limited | Water & waste | 2005 |
| Mavilex Limited | Hospitality | 2012 |
| Maxify ME Ltd | Wholesale & retail | 2025 |
| Maxim Automotive & Motorsports Consultancy Limited | Professional & scientific | 2013 |
| Maximum Demand Limited | Construction | 2012 |
| Mayalland Ltd | Wholesale & retail | 2017 |
| Maycroft Dental Care Limited | Health & social care | 2012 |
| Maydeb Court RTM Company Limited | Households | 2020 |
| Maz-Pom Limited | Health & social care | 2022 |
| MC Accountancy Limited | Financial services | 2017 |
| MC Financial Training Ltd | Education | 2013 |
| Mcdonald Building Engineers Limited | Professional & scientific | 2014 |
| Mcgregor Railway Services Ltd. | Administrative & support | 1996 |
| Mckens Limited | Health & social care | 2022 |
| Mcld Plumbing Ltd | Construction | 2019 |
| Mcmg Business Ltd | Transport & logistics | 2026 |
| Mcmichen Brooks Dental Care Ltd | Health & social care | 2011 |
| MCR Scott Ltd | Wholesale & retail | 2007 |
| Meadcoates Taverns Ltd | Hospitality | 2020 |
| Media Physiques Ltd | Other services | 2019 |
| Medicalworld Care Limited | Health & social care | 2018 |
| Medina Textiles Limited | Real estate | 1990 |
| Medline Services UK Limited | Transport & logistics | 2020 |
| Meduvox Ltd | Education | 2025 |
| Meesons Bluff Limited | Professional & scientific | 2006 |
| Meeting Mojo Ltd | Information & communication | 2011 |
| Mega Choice Support Ltd | Public administration | 2018 |
| Mega Crop Ltd | Professional & scientific | 2014 |
| Megah Holding Ltd | Wholesale & retail | 2023 |
| Megan Apartments Ltd | Real estate | 2018 |
| Megan Trade Ltd | Construction | 2014 |
| MEI Block Ltd | Information & communication | 2021 |
| Memoria - Amber Valley Memorial Park Ltd | Other services | 2013 |
| Memoria - Cardiff & Glamorgan Memorial Park Ltd | Other services | 2011 |
| Memoria - Denbighshire Memorial Park Ltd | Other services | 2015 |
| Memoria - Doncaster Memorial Park Ltd | Other services | 2021 |
| Memoria - Flintshire Memorial Park Ltd | Other services | 2017 |
| Memoria - North Herts Memorial Park Ltd | Other services | 2016 |
| Memoria - North Kent Memorial Park Ltd | Other services | 2022 |
| Memoria - North Oxfordshire Memorial Park Ltd | Other services | 2017 |
| Memoria - Waveney Memorial Park Ltd | Other services | 2014 |
| Memoria Funeral Plans Limited | Other services | 2016 |
| Memoria Funerals Limited | Other services | 2021 |
| Memoria Limited | Construction | 2009 |
| Memsep Filtration Limited | Professional & scientific | 2012 |
| Memsep Holdings Limited | Financial services | 2023 |
| Men-Sorted Ltd | Wholesale & retail | 2025 |
| Menable Group Ltd | Professional & scientific | 2020 |
| Messenger Enterprises Limited | Wholesale & retail | 2003 |
| Metalshak Limited | Arts & recreation | 2021 |
| Metcalf Security Group Ltd | Administrative & support | 2019 |
| Method 8 Ltd | Other services | 2024 |
| Methven Properties Ltd | Real estate | 2021 |
| Metropolis Properties (Oxford) Ltd | Construction | 2024 |
| Metroworks Limited | Professional & scientific | 2018 |
| Mezger Limited | Wholesale & retail | 2023 |
| MF Productions Ltd | Arts & recreation | 2006 |
| Mfhw Holdings Ltd | Financial services | 2026 |
| Mfhw Properties Ltd | Real estate | 2026 |
| MG & Sons Property Investment Ltd | Real estate | 2024 |
| Mgrill Ltd | Hospitality | 2026 |
| MGX Automobiles Limited | Wholesale & retail | 2026 |
| MGX Studios Limited | Information & communication | 2026 |
| Mhayak Limited | Real estate | 2025 |
| Mi-Coffeesolutions Limited | Manufacturing | 2026 |
| MIA Pinhole Cameras Ltd | Manufacturing | 2022 |
| Micandboy Limited | Construction | 1985 |
| Miccl Limited | Education | 2023 |
| Michael Brown Consulting Ltd | Professional & scientific | 2019 |
| Michelle Niziol Ltd | Real estate | 2018 |
| Micrographix Ltd | Administrative & support | 2024 |
| MICROSCOPY101 Ltd | Professional & scientific | 2015 |
| Microtom Limited | Information & communication | 2017 |
| Middle Aston Pet Supplies Ltd | Wholesale & retail | 2025 |
| Mike Holdsworth Limited | Professional & scientific | 2005 |
| Mike Nugent Limited | Construction | 2013 |
| Mike Pearse Holdings Limited | Construction | 2016 |
| Mike&Georgia Property Ltd | Real estate | 2023 |
| Mikulska Management Consultancy Ltd | Real estate | 2011 |