| M&M Beverages Ltd | Wholesale & retail | 2022 |
| M&M Building Trade Ltd | Real estate | 2024 |
| M&M Cash and Carry Ltd | Wholesale & retail | 2025 |
| M&P Property Rentals Limited | Real estate | 2021 |
| M&S Food Hub Limited | Hospitality | 2025 |
| M&S Pro Ground Solutions Ltd | Wholesale & retail | 2025 |
| M-Bar. Consulting Limited | Real estate | 2017 |
| M-Line Automotive Services Ltd | Wholesale & retail | 2015 |
| M. Delacey and Sons (Dowlais) Limited | Wholesale & retail | 1978 |
| M.A. Rees Construction Limited | Construction | 1998 |
| M.A.D. Commercials Limited | Wholesale & retail | 2015 |
| M.A.N Housing & Property Services Ltd | Real estate | 2026 |
| M.A.Q Design Ltd. | Professional & scientific | 2016 |
| M.E. Medical Education Consultancy Ltd | Education | 2011 |
| M.H.L. Residents Association Limited | Households | 1985 |
| M.O.D. Construction Services Limited | Construction | 2021 |
| M.R Pontypool Ltd | Hospitality | 2016 |
| M.S.S. Newport Ltd | Hospitality | 2015 |
| M.T.C. & Associates Limited | Wholesale & retail | 1985 |
| M.U.G.S. Limited | Transport & logistics | 2009 |
| M3MAS Limited | Professional & scientific | 2014 |
| M4MERCURIAL Limited | Professional & scientific | 2018 |
| M4PC Limited | Real estate | 2009 |
| M5 Associates Limited | Financial services | 2005 |
| MA PR Ltd | Professional & scientific | 2022 |
| MA Somerton Fish Bar Ltd | Hospitality | 2023 |
| Ma.Hasnain Enterprise Ltd | Financial services | 2026 |
| MA5 Promotions Ltd | Arts & recreation | 2020 |
| Maabr Limited | Wholesale & retail | 2012 |
| Mabli Homes Ltd | Real estate | 2024 |
| MAC & Co Property Ltd | Real estate | 2024 |
| Machinesource Limited | Professional & scientific | 2025 |
| Mackenzies Accountants Limited | Professional & scientific | 1998 |
| Mackflook Holdings Ltd | Real estate | 2018 |
| Mackhouses Ltd | Real estate | 2025 |
| Macward Steel Slitting Services Limited | Manufacturing | 1975 |
| MAD Dog PUB Co Limited | Wholesale & retail | 2019 |
| MAD on Models Limited | Wholesale & retail | 2009 |
| Maddison Payroll Services Limited | Professional & scientific | 2012 |
| Made for YOU Events by Ayesha Ltd | Other services | 2026 |
| Made Roughley Ltd | Information & communication | 2025 |
| Made With a Cwtch CYF | Wholesale & retail | 2024 |
| Madecause Limited | Real estate | 1988 |
| Madeira Court (Bonchurch) Management Company Limited | Households | 1988 |
| Mademanvans Ltd | Transport & logistics | 2025 |
| Madgwick Park Management Company Limited | Households | 2019 |
| Madness Limited | Other services | 2019 |
| Madol Limited | Wholesale & retail | 1990 |
| Madziro Properties Ltd | Real estate | 2024 |
| Maesglas Sports & Social Club Ltd | Hospitality | 2025 |
| Maeve Property Staging Ltd | Professional & scientific | 2025 |
| MAF Cosmetic Consultants Ltd | Professional & scientific | 2023 |
| Maff Transport Ltd | Transport & logistics | 2024 |
| MAG Bricklaying Limited | Construction | 2020 |
| Magen Ltd | Administrative & support | 2017 |
| Magen Property Investment Limited | Real estate | 2024 |
| Magic Bloom Decors Ltd | Other services | 2025 |
| Magic Kingdom Limited | Manufacturing | 1995 |
| Magical Traveller Ltd | Administrative & support | 2019 |
| Magichands Physiotherapy Ltd | Health & social care | 2016 |
| Magicians 3D Limited | Manufacturing | 2026 |
| Magmatic Stories Cwmni Buddiant Cymunedol | Information & communication | 2023 |
| Magna Porta Ltd. | Real estate | 2024 |
| Magna Transport Planning Ltd | Professional & scientific | 2022 |
| Magnet Creative Design Limited | Other services | 1997 |
| Magnetree Properties Ltd | Real estate | 2023 |
| Magnitt Ventures Ltd | Information & communication | 2024 |
| Magnolia Court (Isle of Wight) Management Company Limited | Households | 2003 |
| Magnolia Drive Limited | Households | 2013 |
| Magnumdot Ltd | Wholesale & retail | 2023 |
| Magnus Tech Limited | Professional & scientific | 2025 |
| Magor Motor Company 2023 Limited | Wholesale & retail | 2023 |
| Mags Air Ltd | Manufacturing | 2016 |
| MAH Drywall Ltd | Construction | 2018 |
| MAH Drywall S/W Ltd | Construction | 2024 |
| MAH Group S/W Ltd | Financial services | 2024 |
| Mahadeventerprisebristol Limited | Wholesale & retail | 2025 |
| Mahin Spice NPT Ltd | Hospitality | 2022 |
| Mahiya Living Ltd | Construction | 2024 |
| Mahoney Consulting Limited | Information & communication | 2010 |
| Mahw Investments Ltd | Real estate | 2025 |
| Maid to Help Cleaning Specialists Ltd | Administrative & support | 2021 |
| Maid to Help Construction Ltd | Administrative & support | 2026 |
| Maid to Help Group Ltd | Financial services | 2026 |
| Maid to Help Security Ltd | Administrative & support | 2026 |
| MAID2CLEAN (Perfect) Ltd | Households | 2022 |
| Maidment Flooring Limited | Construction | 2002 |
| Mailweb Services Limited | Professional & scientific | 1999 |
| Maindee Fresh Food Traders Ltd | Wholesale & retail | 2024 |
| Mainstream Motor Company Ltd | Wholesale & retail | 2023 |
| Mainstreet Nightclub Ltd | Hospitality | 2021 |
| Mainstreet Property Services Limited | Households | 2004 |
| Mainty Group Consulting Limited | Construction | 2021 |
| Mainty Group Holdings Ltd | Households | 2025 |
| Mair Inc Ltd | Hospitality | 2024 |
| Majdari Ltd | Construction | 2024 |
| Majero Graphics Limited | Information & communication | 2024 |
| Majhad Ltd | Real estate | 2021 |
| Maji Properties Ltd | Real estate | 2022 |
| Major Consultancy Services Limited | Administrative & support | 2025 |