| Mitchell Rayner Ltd | Administrative & support | 2017 |
| Mitech Pro Ltd | Wholesale & retail | 2026 |
| Mitkova Ltd | Professional & scientific | 2024 |
| Mitre Consultants Limited | Administrative & support | 2013 |
| Mittens Plumbing & Heating Ltd | Construction | 2008 |
| Mixtape Reinvented Ltd | Information & communication | 2024 |
| Mixxwell Productions Ltd | Information & communication | 2017 |
| Mj&A Property Holdings Limited | Real estate | 2025 |
| MJB Builders (Croydon) Ltd | Construction | 2023 |
| MJC ENT Ltd | Health & social care | 2026 |
| MJG Bloodstock and Racing Ltd | Professional & scientific | 2023 |
| MJL CAD Limited | Information & communication | 1998 |
| Mjrtpws Ltd | Hospitality | 2025 |
| MJT Dental Limited | Health & social care | 2021 |
| Mjteethart Limited | Health & social care | 2021 |
| MK Tradeco Ltd | Administrative & support | 2013 |
| MKS Services Limited | Health & social care | 2016 |
| ML House Limited | Wholesale & retail | 2019 |
| ML Representation Ltd | Professional & scientific | 2023 |
| MLD Audio Limited | Arts & recreation | 2020 |
| MLD Site Services Ltd | Construction | 2026 |
| Mlel Ltd | Hospitality | 2021 |
| MLL Coffe Limited | Hospitality | 2025 |
| MM Book-Keeping Limited | Professional & scientific | 2005 |
| MM Dental Limited | Health & social care | 2021 |
| MM Properties (Mersea) Limited | Real estate | 2025 |
| Mmaf Limited | Health & social care | 2011 |
| Mmaf Property Ltd | Real estate | 2025 |
| MMS Majithia Investments Limited | Real estate | 2024 |
| MMS Studio Limited | Professional & scientific | 2025 |
| MN Garden Maintenance Limited | Administrative & support | 2005 |
| MN Greenall Ltd | Health & social care | 2008 |
| MNG Electrical Services Ltd | Construction | 2022 |
| Mobea Media Limited | Professional & scientific | 2014 |
| Mobile Cloud International Ltd | Extraterritorial | 2018 |
| Mobile Cloud Limited | Information & communication | 2010 |
| Mobile Digital Insights Limited | Professional & scientific | 2023 |
| Mobius Consult Ltd | Professional & scientific | 2025 |
| Mochara Apparel Ltd | Wholesale & retail | 2019 |
| Mochara International Ltd | Wholesale & retail | 2022 |
| Mochara Ltd | Wholesale & retail | 2022 |
| Modal YEW Ltd | Information & communication | 2024 |
| Mode Musik Limited | Information & communication | 2025 |
| Model Pitch Ltd | Wholesale & retail | 2018 |
| Modern Goddess Zone Ltd | Other services | 2024 |
| MODULO17 Ltd | Information & communication | 2014 |
| Mogal Pratap BN Ltd | Hospitality | 2022 |
| Moira Nangle Associates Limited | Administrative & support | 2008 |
| Molai Bankers PLC | Financial services | 2019 |
| Molino Property (UK) Ltd | Real estate | 2023 |
| Mollys Property Group Ltd | Real estate | 2025 |
| MON Cafe Hove Ltd | Hospitality | 2021 |
| Moncer Capital Limited | Extraterritorial | 2014 |
| Money Advice and Community Support Service | Financial services | 1995 |
| Moneyarch Ltd | Real estate | 2003 |
| Monkeyboy Books Limited | Arts & recreation | 2003 |
| Monkwell Fabrics Limited | Extraterritorial | 2001 |
| Monlex Property Ltd | Real estate | 2025 |
| Monotreme Records Limited | Information & communication | 2002 |
| Monroe Hair Ltd | Other services | 2016 |
| Monster TV Production Limited | Information & communication | 2006 |
| Montague Centre (Gpsec) Ltd | Professional & scientific | 2023 |
| Montbretia Advisory Ltd | Administrative & support | 2024 |
| Monteagle Holdings Limited | Real estate | 2008 |
| Monteagle Trustees Limited | Real estate | 2008 |
| Montefiore Fast Food Ltd | Hospitality | 2021 |
| Montefiore Fisheries Limited | Hospitality | 2017 |
| Montgomery Partners Ltd | Administrative & support | 2011 |
| Montvue Ltd | Information & communication | 2025 |
| Monumenttax Ltd | Professional & scientific | 2022 |
| Monzo Tyres Ltd | Wholesale & retail | 2026 |
| Mood London Ltd | Wholesale & retail | 2021 |
| Moonchip Limited | Other services | 2012 |
| Moondoor Properties Limited | Financial services | 2023 |
| Moonsbrook Alpacas Limited | Agriculture & fishing | 2007 |
| Moonsilver Limited | Wholesale & retail | 2007 |
| Moonstone Asset Management Ltd | Real estate | 2023 |
| Moor House Farm Solar Limited | Energy | 2013 |
| Moor Park Capital Partners LLP | | 2006 |
| Moore Heat (Sussex) Ltd | Construction | 2023 |
| Morell Companionship Ltd | Health & social care | 2025 |
| Morelli Take Away Limited | Hospitality | 2024 |
| Morgan Barrett Ltd | Professional & scientific | 2008 |
| Morgan Fit OUT Ltd | Construction | 2011 |
| Morgan Giles Construction Ltd | Construction | 2023 |
| Mornington Mansions RTM Company Limited | Households | 2019 |
| Moroja Rentals Limited | Real estate | 2025 |
| Morris Works Limited | Manufacturing | 2021 |
| Morristree Limited | Real estate | 2015 |
| Mortgage Medics Limited | Financial services | 2007 |
| Mortimer Risk and Control Ltd | Professional & scientific | 2018 |
| Mortlake Investments Ltd | Real estate | 2019 |
| Morton Solar Limited | Energy | 2014 |
| Morwell Living Limited | Real estate | 2023 |
| Moryas & Hove Limited | Wholesale & retail | 2026 |
| Mother and Daughter Funeral Directors Ltd | Extraterritorial | 2011 |
| Mother Duck Limited | Other services | 2017 |
| Mother Duckers Ltd | Wholesale & retail | 2025 |
| Mother Goose Media Limited | Information & communication | 2009 |
| Motif Systems Limited | Professional & scientific | 2022 |