| MJ Softplay Limited | Administrative & support | 2019 |
| MJD Farming Limited | Agriculture & fishing | 2009 |
| MJS Project Services Ltd | Professional & scientific | 2015 |
| MK Edwards TM Ltd | Construction | 2024 |
| Mkamr Management Ltd | Health & social care | 2021 |
| Ml&S Martin Lynch & Sons Limited | Wholesale & retail | 2000 |
| MLS Consultancy Limited | Professional & scientific | 2002 |
| MM Artists Limited | Arts & recreation | 2004 |
| MM Design (London) Limited | Wholesale & retail | 2009 |
| Mmcc Property Ltd | Construction | 2010 |
| MMD Management Company Limited | Professional & scientific | 2017 |
| MMK Radiology Ltd | Health & social care | 2025 |
| MML LIV Ltd | Financial services | 2018 |
| Mmm&S Ltd | Professional & scientific | 2022 |
| Mobile Cycle Service Limited | Manufacturing | 2009 |
| Mobile Golf Ltd | Arts & recreation | 2024 |
| Mobile Phones Limited | Information & communication | 2007 |
| Mobile Therapist Limited | Administrative & support | 2013 |
| Mocha Chocolate Ltd | Manufacturing | 2020 |
| Mocha Chocolate Shop Ltd | Wholesale & retail | 2003 |
| Mocoffee UK Limited | Wholesale & retail | 2019 |
| Mocss Ltd | Professional & scientific | 2018 |
| Modern Minds Consulting Ltd | Information & communication | 2015 |
| Modify Life Ltd | Other services | 2021 |
| Modrics Surveyors Ltd | Construction | 2018 |
| Moduloft Limited | Construction | 2016 |
| Mohammad Saad Ltd | Wholesale & retail | 2024 |
| Mohr MGMT1 Limited | Households | 2025 |
| Molonlave Ltd | Wholesale & retail | 2023 |
| Moltocorp Ltd | Wholesale & retail | 2023 |
| Momentum Strategy Ltd | Professional & scientific | 2025 |
| Momentum Taxation and Accountancy Ltd | Professional & scientific | 2006 |
| MON Muse Trading Ltd | Wholesale & retail | 2025 |
| Monarj Limited | Information & communication | 2004 |
| Monat Ltd | Information & communication | 2024 |
| Moneypenny Camera Limited | Information & communication | 2022 |
| Monivea Bloodstock Limited | Agriculture & fishing | 2014 |
| Mono RS Ltd | Construction | 2021 |
| Mono Works Ltd | Professional & scientific | 2015 |
| Monolo Studio Ltd | Wholesale & retail | 2018 |
| Monroe Technical Resourcing Limited | Administrative & support | 2015 |
| Monroe’S Jewellers Limited | Wholesale & retail | 2023 |
| Mont Group Limited | Financial services | 2023 |
| Mont Interiors Limited | Administrative & support | 2020 |
| Montrose Ventures Limited | Financial services | 2017 |
| Monument 18 Limited | Real estate | 2023 |
| Moonshine Features Limited | Information & communication | 2020 |
| Moor Park Capital NG Ltd | Administrative & support | 2023 |
| Moorland Biomass Ltd | Agriculture & fishing | 2024 |
| Morales Ventures Ltd | Wholesale & retail | 2026 |
| Moran UX Consulting Limited | Professional & scientific | 2022 |
| Morden Properties Limited | Real estate | 2009 |
| Moreland Property Investments Limited | Real estate | 2021 |
| Morgan Knee Clinic Limited | Health & social care | 2008 |
| Morpheus Prime Ltd | Real estate | 2021 |
| Mosa Care Ltd | Health & social care | 2023 |
| Mosaic Initiative | Other services | 2011 |
| Moss & Campbell Finance Limited | Construction | 1966 |
| Moss House Residents Company Limited | Households | 1985 |
| Moto Connection Ltd | Wholesale & retail | 2011 |
| Motomouse Limited | Information & communication | 2020 |
| Motts Electrical Services Limited | Construction | 2022 |
| Mountainbay Accounting Limited | Professional & scientific | 2025 |
| Mourenza Ltd | Professional & scientific | 2025 |
| Moving Image Europe Ltd | Information & communication | 2019 |
| MP Frylinck Ltd | Information & communication | 2015 |
| MP3 Partnership Ltd | Professional & scientific | 2019 |
| Mparker Consultancy Ltd | Professional & scientific | 2025 |
| MR Loveday Ltd | Information & communication | 2023 |
| MR Sloane London Ltd | Wholesale & retail | 2017 |
| Mrc-Agri Holdings Ltd | Professional & scientific | 2020 |
| Mrc-Agri Ltd | Agriculture & fishing | 2022 |
| MRK Management Limited | Professional & scientific | 2013 |
| MRS Clean Ltd | Administrative & support | 2020 |
| MRT1 Ltd | Hospitality | 2025 |
| MS Curry Ltd | Hospitality | 2017 |
| MS Europe Building Services Ltd | Construction | 2015 |
| Ms&El Properties Ltd | Real estate | 2023 |
| Mskb BVI Ltd | Real estate | 2025 |
| Mskm Services Ltd | Wholesale & retail | 2025 |
| Mtaphelan Ltd | Information & communication | 2018 |
| MTS Estimating Ltd | Professional & scientific | 2017 |
| Mudita Ltd | Administrative & support | 2005 |
| Muhasebem Ltd | Professional & scientific | 2025 |
| Muijser Consulting Limited | Professional & scientific | 2010 |
| Mulqueen Industries Limited | Information & communication | 2024 |
| Mult Box Media Ltd. | Professional & scientific | 2020 |
| Mumbles Ales Syndicate Ltd | Hospitality | 2022 |
| Mundy Cruising Limited | Administrative & support | 1970 |
| Muon Agentic Limited | Information & communication | 2021 |
| Murder Boxx Ltd | Information & communication | 2024 |
| Murphy Capital Limited | Financial services | 2020 |
| Museum of Richmond(The) | Arts & recreation | 1986 |
| Music for Parties Ltd | Administrative & support | 2023 |
| Musidora Management Ltd | Professional & scientific | 2018 |
| MVK Property Group Ltd | Real estate | 2026 |
| MW Intelligence Limited | Information & communication | 2026 |
| MW Northern Property Limited | Real estate | 2019 |
| MX2 Comms Limited | Manufacturing | 2006 |
| My ER Hub Ltd | Information & communication | 2026 |