| Merrifield Road Transport Limited | Real estate | 1964 |
| Methodflex Electrical Ltd | Construction | 2020 |
| Mevo Properties Ltd | Real estate | 2024 |
| Mezmon Limited | Real estate | 2025 |
| MF Beasley Electrical Limited | Construction | 2015 |
| MGD Training Ltd | Education | 2015 |
| MH Equestrian Limited | Professional & scientific | 2015 |
| MHS Building Roofing & Carpentry Ltd | Construction | 2012 |
| MIA Technical Services Limited | Professional & scientific | 2021 |
| Michael MAY Search Ltd | Professional & scientific | 2022 |
| Michael Williams Associates Limited | Professional & scientific | 2003 |
| MID Suffolk Yoga Limited | Arts & recreation | 2011 |
| Midas Cleaning Services Limited | Administrative & support | 2002 |
| Midsummer Tuesday Limited | Real estate | 2025 |
| Mikalan Investments Ltd | Real estate | 2025 |
| Mikami Development UK Limited | Wholesale & retail | 2023 |
| Mikehorw Consulting Limited | Information & communication | 2016 |
| Milbourne Financial Services Limited | Professional & scientific | 2021 |
| Miles Marketing Limited | Professional & scientific | 2019 |
| Milk IT Digital Ltd | Information & communication | 2022 |
| Milk Street Holdings Limited | Extraterritorial | 1872 |
| Milk Street Securities Limited | Extraterritorial | 1966 |
| Mill CRT Harlow Limited | Households | 2024 |
| Mill View Management Company Limited | Households | 1985 |
| Millard Civil Engineering Ltd | Construction | 2025 |
| Millard Property Ltd | Construction | 2013 |
| Millbank Communications Ltd | Professional & scientific | 2023 |
| Millest Investments Ltd | Real estate | 2026 |
| Millowe Ltd | Wholesale & retail | 2019 |
| Mimi Nails and Spa Limited | Other services | 2026 |
| Mimosa Telecoms Ltd | Information & communication | 2020 |
| Minds That Work Ltd | Education | 2022 |
| Minh ANH & J Ltd | Other services | 2025 |
| Mint Leaf Spice Ltd | Hospitality | 2025 |
| Mirrormedia Limited | Manufacturing | 2004 |
| Mirrortv Limited | Professional & scientific | 2004 |
| MIS Sold Sipp Ltd | Real estate | 2015 |
| Miss Cote D'Ivoire UK Limited | Arts & recreation | 2025 |
| Miss Emma Walsh Ltd | Arts & recreation | 2023 |
| Mitch Corporation Ltd | Wholesale & retail | 2022 |
| Mitchell Farrar Property LLP | | 2015 |
| Miteflux Technologies Ltd | Information & communication | 2025 |
| MJF Rail Ltd | Transport & logistics | 2026 |
| MJG Property Services (London) Ltd | Other services | 2021 |
| MJW Technology Solutions Limited | Information & communication | 2025 |
| Mjwr Ltd | Professional & scientific | 2012 |
| MKK Lion Ltd | Information & communication | 2022 |
| Mkrec Limited | Administrative & support | 2018 |
| MLD Studio Ltd | Professional & scientific | 2015 |
| MMG Counselling and Consultancy Ltd | Health & social care | 2020 |
| Mmjs Services Ltd | Professional & scientific | 2017 |
| Mobe Digital Ltd | Information & communication | 2019 |
| Mobile Motors Essex Limited | Wholesale & retail | 2020 |
| Mobnationuk Ltd | Wholesale & retail | 2020 |
| Mobo Solutions Ltd | Information & communication | 2025 |
| Mocha 28 Ltd | Other services | 2024 |
| Modern Movements 25 Ltd | Wholesale & retail | 2025 |
| Moirai Consulting Limited | Professional & scientific | 2016 |
| Molina Lifestyle Ltd | Wholesale & retail | 2025 |
| Molseb Investments Limited | Administrative & support | 2017 |
| Momentum Sales Progression Ltd | Administrative & support | 2024 |
| Monch Estate Limited | Real estate | 2016 |
| Monika Bakonyi Therapy Ltd | Health & social care | 2023 |
| Monkey Aviation Limited | Manufacturing | 2007 |
| Monkey Planet Limited | Extraterritorial | 2005 |
| Montpellier Property Group Ltd | Real estate | 2024 |
| Monty's Photography Limited | Professional & scientific | 2008 |
| Moorgate Consultancy Ltd | Professional & scientific | 2020 |
| Morale Properties Ltd | Real estate | 2019 |
| More Than Words Ltd | Professional & scientific | 2026 |
| Morelli Enterprises Ltd | Other services | 2012 |
| Morre Waste Ltd | Water & waste | 2021 |
| Morris Jane Associates Ltd | Administrative & support | 2017 |
| Mosaic Hair & Beauty Studio Limited | Other services | 2003 |
| Moss Productions Limited | Information & communication | 2021 |
| Mossy LEA Farm LLP | | 2012 |
| Most Wanted Books Limited | Wholesale & retail | 2025 |
| Moult Walker Limited | Professional & scientific | 1998 |
| Moult Walker Surveyors Limited | Real estate | 2018 |
| Moyd Ltd | Information & communication | 2025 |
| Mozaiq Consulting Ltd | Information & communication | 2017 |
| MR Barbers (Logo) Limited | Extraterritorial | 2016 |
| MR Barbers Products Limited | Wholesale & retail | 2017 |
| MR Barbers Topco Ltd | Other services | 2017 |
| MR Kurt Limited | Professional & scientific | 2026 |
| MR Lawrence Limited | Administrative & support | 1998 |
| MR M Trades Ltd | Professional & scientific | 2022 |
| MR. Lawrence Wine Merchant Limited | Wholesale & retail | 2002 |
| MS Apparel and Textile Mills Private Limited | Manufacturing | 2023 |
| MS Decor & Design Ltd | Construction | 2023 |
| MS Nexus Ltd | Professional & scientific | 2026 |
| MSA Electrical Limited | Construction | 2017 |
| MSM Business Consultants Limited | Financial services | 1995 |
| MSM Engineering Ltd | Manufacturing | 2015 |
| Muda Architecture Ltd | Professional & scientific | 2019 |
| Mulberry Information Systems Limited | Information & communication | 2006 |
| Mullucks Limited | Real estate | 2004 |
| Multi Layer Media Ltd | Professional & scientific | 2013 |
| Multi-Tec Group Ltd | Professional & scientific | 2024 |
| Multivend UK Limited | Wholesale & retail | 1999 |