| Meal Dash Limited | Hospitality | 2025 |
| Mechanify Ltd | Wholesale & retail | 2025 |
| Mediconflex Ltd | Professional & scientific | 2022 |
| Mega Mouse Ventures Ltd | Financial services | 2025 |
| Mela Siop CYF. | Wholesale & retail | 2025 |
| Melrose Tattoo Company Limited | Arts & recreation | 2025 |
| Memorylab Limited | Wholesale & retail | 2014 |
| Menshen Packaging UK Limited | Administrative & support | 1993 |
| Meridian (Penarth Haven) Management Company Limited | Households | 1998 |
| Meridian Health Systems Ltd | Information & communication | 2026 |
| Metron Wrought Ironwork Limited | Construction | 2021 |
| Metson Property Ltd | Real estate | 2018 |
| MH Fire & Security Limited | Administrative & support | 2023 |
| Miahbe Ltd | Wholesale & retail | 2020 |
| Middlepatch Limited | Health & social care | 1987 |
| Mike Gentile Jewellery & Watch Repairs Ltd | Wholesale & retail | 2021 |
| Milestones Group Limited | Education | 2017 |
| Minerva Model Railways Limited | Manufacturing | 2014 |
| Minxiang Limited | Manufacturing | 2025 |
| Mission Discovery Limited | Education | 2014 |
| Mitchell Carter Contracting Limited | Construction | 2023 |
| Mitigate IT Limited | Professional & scientific | 2025 |
| MJB Carpentry Ltd | Construction | 2022 |
| MK Computech Ltd | Information & communication | 2012 |
| MK Penmark Limited | Health & social care | 2005 |
| MKH Decorators Ltd. | Construction | 2025 |
| Mobile Festivals Ltd | Administrative & support | 2026 |
| Mobilefixer Ltd | Other services | 2020 |
| Moderma Limited | Health & social care | 2025 |
| Moesol Consulting Ltd | Information & communication | 2006 |
| Monkstone Court Management Ltd | Extraterritorial | 2012 |
| Monroe Holdings Limited | Real estate | 2021 |
| Montague Place (L1) Limited | Education | 2004 |
| Montague Place (W1) Limited | Education | 2006 |
| Montague Place (Y1) Limited | Education | 2006 |
| Montague Place Limited | Education | 2004 |
| Monty Smith (Cardiff) Ltd | Wholesale & retail | 2016 |
| Moorby Court Management Limited | Households | 2003 |
| Moral Injury Partnership CIC | Health & social care | 2023 |
| Moralis Design Ltd | Professional & scientific | 2021 |
| Moreton Brothers Ltd | Information & communication | 2024 |
| Morgan James Media Limited | Arts & recreation | 2015 |
| Morgan Medical Limited | Administrative & support | 2015 |
| Morgan Property Management Services Ltd | Real estate | 2018 |
| Morgan Spencer Smart Limited | Financial services | 2014 |
| Morgan's Confectionary Ltd | Wholesale & retail | 2024 |
| Morhill 1 Ltd | Real estate | 2025 |
| Morse Affiliated Ltd | Administrative & support | 2018 |
| Morston Solutions Ltd | Real estate | 2025 |
| Mount Stuart Media Limited | Information & communication | 2010 |
| Mount Stuart Square Developments Limited | Real estate | 2018 |
| Move Well Coach Ltd | Health & social care | 2022 |
| MPJ Comms Ltd | Administrative & support | 2024 |
| MRK Restaurant Ltd | Hospitality | 2025 |
| MSA Mining Consulting Ltd | Financial services | 2022 |
| MSA Mining Consulting UK Ltd | Professional & scientific | 2022 |
| MST Solutions Ltd | Construction | 2026 |
| MT1 Construction Ltd | Construction | 2014 |
| MT1 Property Ltd | Real estate | 2017 |
| Muhz Ltd | Professional & scientific | 2025 |
| Mulberry Advisory Ltd | Financial services | 2026 |
| Mulenga Electric Limited | Energy | 2025 |
| Mullaney Medical Services Ltd | Health & social care | 2012 |
| Muscle Dynamic Ltd | Administrative & support | 2009 |
| MWH Consultants Limited | Information & communication | 2012 |
| MWJ Electrical Contractors Ltd | Construction | 2024 |
| My Lighthouse Ltd | Health & social care | 2023 |
| My Lon-Dom Ltd | Real estate | 2016 |
| My Numerology Life Path Ltd | Information & communication | 2025 |
| Myomniverse Ltd | Information & communication | 1969 |
| N & O Investments Limited | Real estate | 2022 |
| N Luke Aviation Ltd | Transport & logistics | 2025 |
| N.G. Reynolds Builders Limited | Construction | 1986 |
| N.O.P. Holdings Limited | Professional & scientific | 2000 |
| Naeem Property Group Limited | Real estate | 2025 |
| Naios Architects Limited | Professional & scientific | 2026 |
| Nantllan Storage and Transport Ltd. | Administrative & support | 2019 |
| Nash Point Brewing Company Limited | Manufacturing | 2025 |
| National Brass Band Championships of Great Britain Ltd | Information & communication | 2011 |
| National Piers Society Limited | Other services | 2005 |
| Natural Eco Vision Ltd | Energy | 2021 |
| NBM Holdings Limited | Financial services | 2017 |
| NBM Management Limited | Administrative & support | 2021 |
| NC & JC Holdings Limited | Real estate | 2024 |
| Neat Sweet Feet Limited | Health & social care | 2018 |
| Neco Electrical UK Company Limited | Manufacturing | 2002 |
| Neco Fire Gard Limited | Manufacturing | 2017 |
| Neco Limited | Administrative & support | 2012 |
| Neco Motors Limited | Extraterritorial | 2012 |
| Nell's Point Barry Ltd | Construction | 2018 |
| Neos Recruitment Ltd | Administrative & support | 2023 |
| NET Zero Heating Solutions LLP | | 2024 |
| Newmar Properties Limited | Real estate | 2015 |
| Newmar Restaurants Limited | Hospitality | 2015 |
| NIC Hooper Psychological Services Ltd | Education | 2024 |
| Nicholas Carlton Consulting Limited | Professional & scientific | 2021 |
| Nicoll Lettings Ltd | Real estate | 2026 |
| Nigel Arnold Limited | Professional & scientific | 2007 |
| Nightingales Preschool Limited | Education | 2011 |
| Nikki Wilson Ltd | Information & communication | 2022 |