| M S Chilled Foods Ltd | Wholesale & retail | 2002 |
| M S Planning Ltd | Professional & scientific | 2012 |
| M S Portfolio Ltd | Real estate | 2024 |
| M Samuel Rail Limited | Manufacturing | 2018 |
| M Sayers Bespoke Joinery Ltd | Manufacturing | 2025 |
| M Skelly Driving Ltd | Transport & logistics | 2019 |
| M Skelton Ltd | Professional & scientific | 2014 |
| M Taher & Co Ltd | Professional & scientific | 2014 |
| M Thomas Water Services Ltd | Construction | 2000 |
| M W Decor Ltd | Construction | 2021 |
| M W Turner Limited | Health & social care | 2013 |
| M WKD Ltd | Construction | 2024 |
| M&4B Group Ltd | Wholesale & retail | 2026 |
| M&A Creative Couriers Ltd | Transport & logistics | 2026 |
| M&A Motors Cardiff Ltd | Wholesale & retail | 2025 |
| M&A Solicitors LLP | | 2004 |
| M&A Universal Construction Ltd | Construction | 2024 |
| M&A Ventures PVT Ltd | Transport & logistics | 2024 |
| M&C Quality Builders Ltd | Construction | 2019 |
| M&D and R&R LLP | | 2024 |
| M&F London Services Ltd | Construction | 2026 |
| M&F SW Home Improvements Limited | Wholesale & retail | 2019 |
| M&G Barry Consulting Limited | Professional & scientific | 2010 |
| M&H Driveway Landscaping Ltd | Administrative & support | 2026 |
| M&I Finance Limited | Professional & scientific | 2022 |
| M&K Property Cardiff Limited | Real estate | 2024 |
| M&K Property Management Ltd | Real estate | 2016 |
| M&L Construction (Cardiff) Ltd | Construction | 2009 |
| M&M and Associates Limited | Health & social care | 2020 |
| M&M Capital Management Ltd | Wholesale & retail | 2023 |
| M&M Games Ltd | Wholesale & retail | 2025 |
| M&M Holding Group Ltd. | Wholesale & retail | 2021 |
| M&M International Estates Limited | Real estate | 2020 |
| M&M Painting Services Ltd | Construction | 2025 |
| M&M Prop UK Ltd | Real estate | 2019 |
| M&M Tutoring Services Ltd | Education | 2021 |
| M&M Tyre Service Ltd | Wholesale & retail | 2025 |
| M&M WS Limited | Transport & logistics | 2023 |
| M&N Medico Ltd | Health & social care | 2017 |
| M&O Bespoke Fabrications Ltd | Manufacturing | 2018 |
| M&O Contractors Ltd | Construction | 2018 |
| M&O Partners Ltd | Wholesale & retail | 2025 |
| M&R Global Ltd | Wholesale & retail | 2025 |
| M&R Property Management Ltd | Real estate | 2021 |
| M&Re Maintenance Ltd | Construction | 2025 |
| M&S Brain Holdings Ltd | Financial services | 2025 |
| M&S Ecommerce (UK) Ltd | Wholesale & retail | 2024 |
| M&T Manufacturing Ltd | Manufacturing | 2017 |
| M&T Project Management Consultants Ltd | Professional & scientific | 2024 |
| M&V Bespoke Memorials Ltd | Manufacturing | 2019 |
| M&V London Ltd | Wholesale & retail | 2018 |
| M&W Shop LLP | | 2025 |
| M&Wf Ltd | Wholesale & retail | 2025 |
| M&Y Barbers Ltd | Other services | 2019 |
| M&Y Catering Ltd | Hospitality | 2019 |
| M&Z Estates Ltd | Hospitality | 2019 |
| M&Z London Ltd | Wholesale & retail | 2024 |
| M-Donay Express Ltd | Manufacturing | 2015 |
| M-Planning Ltd | Administrative & support | 2010 |
| M-Promax Ltd | Information & communication | 2022 |
| M-Tangoling Ltd | Wholesale & retail | 2019 |
| M-Zee Motors Limited | Wholesale & retail | 2022 |
| M. & M. Lowloaders Limited | Transport & logistics | 1979 |
| M.A.C.K Renewables Ltd | Construction | 2024 |
| M.A.Rapport & Co.Limited. | Wholesale & retail | 1922 |
| M.A.T Welding and Fabricating Services Ltd | Manufacturing | 2024 |
| M.A.W Electrical Contractors Limited | Construction | 2018 |
| M.D. Fabrications Limited | Manufacturing | 1981 |
| M.D. Realisations Limited | | 1937 |
| M.D.G.P.Investments Limited | Professional & scientific | 1962 |
| M.D.T. Electrical Limited | Construction | 2003 |
| M.E. Direct Ltd | Manufacturing | 2023 |
| M.E. Foley (Contractors) Limited | Construction | 1987 |
| M.E.I. Unitech Limited | Manufacturing | 1988 |
| M.E.P. Restaurants Limited | Hospitality | 2019 |
| M.F. O'Malley Formwork Limited | | 1982 |
| M.G Suppliers Ltd | Wholesale & retail | 2021 |
| M.Galaxy.N Ltd | Wholesale & retail | 2025 |
| M.Goldblatt Limited | Wholesale & retail | 1955 |
| M.J. Dean Plastering and Building Ltd | Professional & scientific | 2013 |
| M.J. Harris Repairs Ltd | Other services | 2009 |
| M.J. Richard Corporate Consultancy Services Ltd | Professional & scientific | 2017 |
| M.J.S. Consulting Limited | Professional & scientific | 1997 |
| M.K Cargo Limited | Transport & logistics | 2018 |
| M.K Mail & Logistics Limited | Transport & logistics | 2008 |
| M.K.I Accessories Ltd | Wholesale & retail | 2018 |
| M.K.S Maintenance Ltd | Energy | 2020 |
| M.L Recovery Ltd | Administrative & support | 2019 |
| M.M.K. Carpentry & Joinery Limited | Construction | 2018 |
| M.Maxim Limited | Health & social care | 2019 |
| M.N Engineering Ltd | Manufacturing | 2015 |
| M.N Engineering Solutions Ltd | Construction | 2025 |
| M.P IT Consultancy Services Ltd | Information & communication | 2025 |
| M.P. Business Analysis Limited | Professional & scientific | 2017 |
| M.Poladi Limited | Wholesale & retail | 2026 |
| M.R Electrical & Plumbing Ltd | Construction | 2025 |
| M.R.S. Communications Limited | Information & communication | 1978 |
| M.S. Steel Framed Buildings Ltd | Manufacturing | 2018 |
| M.S.R Restaurants Ltd | Hospitality | 2025 |
| M.Sohaib ALI Ltd | Wholesale & retail | 2026 |