| MKT Global Trading Ltd | Wholesale & retail | 2025 |
| MLC Communications Ltd | Construction | 2024 |
| MLH Services Ltd | Construction | 2023 |
| Mlpro Commercial Cleaning Services Ltd | Administrative & support | 2025 |
| MLV Limited | Health & social care | 2022 |
| MM Estate Investments Limited | Real estate | 2025 |
| MM Glass Ltd | Construction | 2016 |
| MM Targoni Ltd | Construction | 2016 |
| MME Maintenance Ltd | Construction | 2023 |
| MMJ Catering Ltd | Hospitality | 2025 |
| MMR Accountancy Services Limited | Professional & scientific | 2025 |
| MN Security K9 Wear Ltd | Wholesale & retail | 2025 |
| Mndset+ Ltd | Professional & scientific | 2024 |
| MNS Hastings Ltd | Hospitality | 2025 |
| MNS Hospitality Ltd | Hospitality | 2021 |
| MNS Hotel Management Ltd | Hospitality | 2022 |
| Mobile PC UK Limited | Information & communication | 2024 |
| Mobius Healthcare Limited | Wholesale & retail | 2020 |
| Mod-Tech Consultancy Limited | Professional & scientific | 2007 |
| Modas Technology Limited | Information & communication | 2018 |
| Modern Glass & Mirrors Ltd | Manufacturing | 2014 |
| Modern Tradesman Ltd | Construction | 2025 |
| Modi Motors Ltd | Wholesale & retail | 2025 |
| Modulor 123 Ltd | Construction | 2024 |
| Moduu Living Limited | Manufacturing | 2022 |
| Mohamed Saleh Limited | Construction | 2018 |
| Mohammed Riaz Properties Limited | Real estate | 2018 |
| Moir Technical Services Limited | Professional & scientific | 2009 |
| Moisa Services Ltd | Transport & logistics | 2019 |
| Moisantrans Ltd | Wholesale & retail | 2010 |
| Molaton Corporate Services Ltd | Information & communication | 2026 |
| Molbiotech Ltd | Professional & scientific | 2021 |
| Mollisigns Limited | Other services | 2008 |
| Moltek Consultants Limited | Information & communication | 1995 |
| Momentum Results LLP | | 2008 |
| Mominto Ltd | Manufacturing | 2025 |
| Mondo Perfecto Ltd | Construction | 2016 |
| Monest Limited | Financial services | 2016 |
| Mono Lisa Ltd | Wholesale & retail | 2026 |
| Monster Dog Limited | Information & communication | 2021 |
| Montague Green (Rowland's Castle) Management Company Limited | Households | 2017 |
| Montana Communications Limited | Professional & scientific | 1997 |
| Montana Group Limited | Wholesale & retail | 2018 |
| Monterasufilms Ltd | Information & communication | 2020 |
| Montgomery Place Management Company Limited | Households | 2022 |
| Montt Capital LLP | | 2024 |
| Monty Spinning Cobra Limited | Administrative & support | 2006 |
| Moomin Limited | Real estate | 2025 |
| Moonien Limited | Professional & scientific | 2019 |
| Moore Talent Solutions Limited | Administrative & support | 2022 |
| Moore's (Hemel Hempstead) Limited | Wholesale & retail | 1959 |
| Moores & Co Developments Limited | Construction | 2020 |
| Moores & Co Holdings Limited | Financial services | 2020 |
| Moores & Co Investments Limited | Real estate | 2020 |
| Moorhead Richardson Ltd | Professional & scientific | 2018 |
| Moorlands Place Residents Management Company Limited | Households | 2002 |
| More Assets Ltd | Real estate | 2026 |
| Moregreen Energy Limited | Manufacturing | 2015 |
| Moreton Construction Limited | Construction | 2017 |
| Moreton Fields (Buckingham) Residents Management Company Limited | Households | 2025 |
| Morgan Rose Probate Services Ltd | Professional & scientific | 2014 |
| Morgan-Smith Electronics Limited | Real estate | 1974 |
| Morjaria Properties LLP | | 2025 |
| Morphology Consultants Limited | Professional & scientific | 2008 |
| Morrisby Ltd | Information & communication | 1974 |
| Morrisby Trustees Ltd | Professional & scientific | 2023 |
| Morrison & Clooney Limited | Real estate | 2018 |
| Morrissey RC Frames & Groundworks Ltd | Construction | 2013 |
| Mortgage Assist Specialist Ltd | Financial services | 2020 |
| Mortgage Search Ltd | Administrative & support | 2015 |
| Mortimer Isaacs Consultancy LLP | | 2006 |
| Mortlock Securities Ltd | Wholesale & retail | 2018 |
| Mortlock Simmonds Limited | Professional & scientific | 2000 |
| Morton Oak Management Company Limited | Households | 2014 |
| Moshgroup Ltd | Other services | 2018 |
| Mossbank Place Management Company Limited | Real estate | 2018 |
| Mothercare (Holdings) Limited | Administrative & support | 1976 |
| Mothercare Employees' Share Trustee Limited | Financial services | 1976 |
| Mothercare Finance (2) Limited | Professional & scientific | 2020 |
| Mothercare Finance Limited | Administrative & support | 1978 |
| Mothercare Global Brand Limited | Wholesale & retail | 2019 |
| Mothercare Group Limited(The) | Professional & scientific | 1927 |
| Mothercare PLC. | Wholesale & retail | 1985 |
| Mothercare Services Limited | Wholesale & retail | 1983 |
| Motor RAG Media Limited | Information & communication | 2026 |
| Motorcar Tech Services Limited | Information & communication | 2025 |
| Motorcycle Service Centre Limited | Wholesale & retail | 2015 |
| Mototom Cars Ltd | Wholesale & retail | 2017 |
| Mototom Vans Ltd | Wholesale & retail | 2025 |
| Motzo Ltd | Wholesale & retail | 2024 |
| Mountgold Commercial Property Limited | Real estate | 2020 |
| Mountgold Lettings Ltd | Real estate | 2021 |
| Mountgold Rentals LLP | | 2016 |
| Mountgold Watford RD Limited | Real estate | 2021 |
| Mountjoy 1 Limited | Arts & recreation | 2022 |
| Mousseux Ltd | Construction | 2021 |
| Moving London Removals Ltd | Transport & logistics | 2024 |
| Moxon Holdings Ltd | Real estate | 2018 |
| MP Building Improvements Limited | Construction | 2023 |
| MP Property and Developments Ltd | Construction | 2018 |