| MJV Location Services Ltd | Information & communication | 2026 |
| MK Logistics Ltd | Transport & logistics | 2022 |
| MKB Carpets Limited | Wholesale & retail | 2012 |
| MKP Finance Limited | Financial services | 2026 |
| Mkte Ltd | Hospitality | 2026 |
| Mkvales Ltd | Hospitality | 2026 |
| ML & JD Maison Rental Limited | Real estate | 2025 |
| MLC Technology Limited | Professional & scientific | 1998 |
| MLM Transport Ltd | Transport & logistics | 2016 |
| MLP Civils Limited | Construction | 2016 |
| MLS Photography UK Ltd | Manufacturing | 2025 |
| Mlshaw Maintenance Ltd | Construction | 2023 |
| MM Asset Management Ltd | Real estate | 2020 |
| MM Enterprise Group Ltd | Construction | 2025 |
| MM Marine Survey Ltd | Wholesale & retail | 2017 |
| MM Materials Ltd | Construction | 2023 |
| MM Rheoli Gwasanaethau CYF | Construction | 2019 |
| Mm&M Services Ltd | Transport & logistics | 2020 |
| MM2 Electrical Limited | Manufacturing | 2024 |
| MM7 Properties Limited | Real estate | 2024 |
| MMM Consultancy Services Ltd | Information & communication | 2025 |
| MMM Newport Limited | Hospitality | 2023 |
| Mmscorpuz Limited | Real estate | 2025 |
| Mmww Property Ltd | Real estate | 2021 |
| Mmxv Promotions Ltd | Arts & recreation | 2020 |
| MN Health Consultancy Ltd | Education | 2021 |
| MN LPG Training Ltd | Professional & scientific | 2010 |
| MNC Enterprises Ltd | Other services | 2024 |
| Mndst Media Ltd | Professional & scientific | 2025 |
| Mo's Boxing and Fitness Academy Ltd | Arts & recreation | 2010 |
| Mo-Lex Ltd | Information & communication | 2022 |
| Mobile HKE Ltd | Hospitality | 2026 |
| Mobile Plant Support Limited | Manufacturing | 2016 |
| MOBILEBARBERS101 Limited | Other services | 2026 |
| Mobility Angels Ltd | Health & social care | 2018 |
| Mobilum Auto Parts Ltd | Wholesale & retail | 2016 |
| Mocoi Ltd | Manufacturing | 2026 |
| Modaatobs Limited | Health & social care | 2019 |
| Modena Foods Ltd | Hospitality | 2021 |
| Modern Dads Unplugged Ltd | Wholesale & retail | 2026 |
| Modern Eco Line Ltd | Wholesale & retail | 2025 |
| Modern Lights Ltd | Wholesale & retail | 2025 |
| Modern Living (IW) Limited | Manufacturing | 2025 |
| Modest Ltd | Construction | 2023 |
| Modest Property Services Ltd | Extraterritorial | 2025 |
| Modikit Limited | Manufacturing | 2023 |
| Modit Limited | Information & communication | 2025 |
| Modu Construction Ltd | Construction | 2026 |
| Modular Site Services Ltd | Construction | 2023 |
| Mogfords Hardware Ltd | Wholesale & retail | 2026 |
| Moggzy Delivers Limited | Transport & logistics | 2025 |
| Mohsin ALI Ltd | Wholesale & retail | 2025 |
| Moirai Folio Ltd | Arts & recreation | 2003 |
| Mojo Rising Limited | Wholesale & retail | 2017 |
| Moka Trading Ltd | Wholesale & retail | 2021 |
| Molila Project Services Ltd | Construction | 2017 |
| Mollio Limited | Professional & scientific | 2017 |
| Mollov-Executive-Travel Limited | Transport & logistics | 2025 |
| Moloce Transport Ltd | Transport & logistics | 2020 |
| Molyn Limited | Construction | 2014 |
| Momentum Living Ltd | Wholesale & retail | 2025 |
| Momentum Sportswear Ltd | Wholesale & retail | 2025 |
| Momokakkoii Ltd | Wholesale & retail | 2019 |
| Momoplus+ Ltd | Hospitality | 2025 |
| Monarch Strategy Ltd | Professional & scientific | 2026 |
| Monarchs Keep (Bursledon) Management Company Limited | Households | 2017 |
| Monday Creative Ltd | Professional & scientific | 2014 |
| MONEDDY2 Ltd | Health & social care | 2016 |
| Monex Cranes Limited | Transport & logistics | 2003 |
| Monex Distribution Ltd. | Transport & logistics | 1975 |
| Monex Group Ltd. | Transport & logistics | 2014 |
| Monex International Logistics Limited | Transport & logistics | 2001 |
| Monex Marine Ltd | Transport & logistics | 2026 |
| Moneyshake Holdings Ltd | Financial services | 2019 |
| Monina Gianan Health Care Ltd | Health & social care | 2022 |
| Moniview Limited | Construction | 2006 |
| Monkeys@High Cross Breakfast & After School Club Ltd | Health & social care | 2022 |
| Monkeys@Marshfield Primary OUT of School Club Ltd | Health & social care | 2022 |
| Monks Brook Dental Ltd | Health & social care | 2021 |
| Monkstone Court (Saundersfoot) Management Limited | Households | 2011 |
| Monmouthshire Building Society Charitable Foundation | Other services | 2000 |
| Monmouthshire Fencing Supplies Ltd | Wholesale & retail | 2016 |
| Monmouthshire HOG Roasts Ltd | Hospitality | 2012 |
| Monmouthshire Medical Limited | Other services | 2019 |
| Monmouthshire Specialist Cars Limited | Wholesale & retail | 2016 |
| Monmouthshire Timber Supplies Limited | Manufacturing | 2004 |
| Monmouthshire, Brecon & Abergavenny Canals Trust Limited | Other services | 1984 |
| Monnow Developments Limited | Real estate | 1973 |
| Monnow Valley Biomass PLC | Administrative & support | 2014 |
| Monnow Valley Studio Limited | Arts & recreation | 2017 |
| Mono Metals Ltd | Wholesale & retail | 2011 |
| Monsoon Indian Bangla Dining Limited | Hospitality | 2011 |
| Monster Repair Shop Limited | Wholesale & retail | 2023 |
| Montana's Enterprise Ltd | Wholesale & retail | 2023 |
| Monte Romano Ltd | Hospitality | 2024 |
| Monzanite Motorsport Ltd | Arts & recreation | 2014 |
| MOO Vaughan Home Ltd | Real estate | 2017 |
| Moobaa Ltd | Wholesale & retail | 2020 |
| Mood Broker Limited | Information & communication | 2024 |
| Moon's Elephant Limited | Hospitality | 2024 |