| MCQ Consultants Ltd | Professional & scientific | 2015 |
| Md-It Limited | Information & communication | 2019 |
| Mdmdata Consult Ltd | Professional & scientific | 2016 |
| Mealtech Limited | Information & communication | 2023 |
| Medavera Technologies Limited | Professional & scientific | 2026 |
| Medixal London Ltd | Wholesale & retail | 2022 |
| Medscripta Limited | Education | 2020 |
| Medtek Ltd | Health & social care | 2018 |
| Megjet Estates Ltd | Real estate | 2025 |
| MEK Construction Limited | Administrative & support | 2011 |
| Mel-Art Construct Ltd | Construction | 2026 |
| Melila Property Management Ltd | Real estate | 2024 |
| Memz Engineering Ltd | Wholesale & retail | 2020 |
| Mentan Ltd | Real estate | 2020 |
| Merc Enterprise Limited | Real estate | 2007 |
| Merry Hill After School Club Ltd | Health & social care | 2025 |
| Merryweather Pets Ltd | Other services | 2019 |
| Metrikus Limited | Information & communication | 2019 |
| Metro Marketing (Europe) Limited | Wholesale & retail | 2010 |
| Metropolitan Police Bushey Sports Club Limited | Arts & recreation | 2008 |
| MG Painting and Decorating Ltd | Construction | 2017 |
| MG Property Ventures Ltd | Real estate | 2024 |
| MGB Rail Limited | Manufacturing | 2014 |
| MI Risk Software Ltd | Information & communication | 2016 |
| MI Risk Technologies Ltd | Information & communication | 2016 |
| Middlesex Property Services Limited | Real estate | 1984 |
| Miella Limited | Manufacturing | 2026 |
| Mika Copy Ltd | Professional & scientific | 2021 |
| Mill Rock Properties Ltd | Hospitality | 2018 |
| Millbrow Limited | Real estate | 1996 |
| Millie MOO Designs Ltd | Wholesale & retail | 2022 |
| Millpress Print & Embroidery Ltd | Wholesale & retail | 2018 |
| Mimram Site Services Limited | Construction | 2002 |
| Mind Gym Therapy Ltd | Health & social care | 2021 |
| Mini Lingos Franchising Limited | Administrative & support | 2024 |
| Mini Nails Bar Ltd | Other services | 2025 |
| Minidraw Limited | Real estate | 1994 |
| Mint Greene Limited | Administrative & support | 2018 |
| Mint Studios London Ltd. | Professional & scientific | 2022 |
| Minutiae Media Ltd | Information & communication | 2024 |
| Mirabel Property Company Limited | Extraterritorial | 1960 |
| Mirechapel Ltd | Real estate | 2013 |
| Mironi Ltd | Wholesale & retail | 2019 |
| Misbourne Developments Ltd | Construction | 2022 |
| Misbourne Residential Ltd | Real estate | 2023 |
| Miss Sunshine Limited | Administrative & support | 2013 |
| Mita TP Consulting Limited | Real estate | 2017 |
| Miyano Machinery UK Limited | Extraterritorial | 1983 |
| MJ Jonni Ltd | Administrative & support | 2022 |
| MKF Homecare Limited | Health & social care | 2014 |
| MMF Brickworks Ltd | Construction | 2020 |
| Moatfield Playgroup Ltd | Education | 2025 |
| Modern Roadtrips Ltd | Administrative & support | 2023 |
| Modus Ventures Limited | Administrative & support | 2016 |
| Moffitt Project Services Ltd | Professional & scientific | 2003 |
| Mojo Uddin Limited | Wholesale & retail | 2025 |
| Momentum Mindset Ltd | Arts & recreation | 2020 |
| Monline UK Limited | Transport & logistics | 2016 |
| Montague Media Ltd | Information & communication | 2023 |
| Montague R Jason (Toys) Limited | Extraterritorial | 1945 |
| Moon Design Ltd | Professional & scientific | 2025 |
| Moonlyfe Ltd | Wholesale & retail | 2025 |
| Moonstone Cafe Ltd | Hospitality | 2026 |
| Morango Media Limited | Information & communication | 2012 |
| Moreandco Ltd | Construction | 2025 |
| Morecambe Bay Eden Hotel Project Company Ltd | Construction | 2019 |
| Morris Roofing & Leadworks Ltd | Construction | 2014 |
| Mortgage Mantra Limited | Financial services | 2015 |
| Motherhood Diaries UK Ltd | Information & communication | 2024 |
| Mothership Entertainment Ltd | Wholesale & retail | 2025 |
| Motionblurr Ltd | Information & communication | 2012 |
| Movequick Limited | Construction | 2018 |
| Moxon Developments Ltd | Construction | 2016 |
| Moxon Investments Ltd | Construction | 2016 |
| MP Tiling Contractor Ltd | Construction | 2018 |
| MPM Engineering Limited | Construction | 2007 |
| MR Puff Pro Ltd | Wholesale & retail | 2022 |
| MRC Heating and Plumbing Limited | Construction | 2014 |
| Mrfd Consulting (UK) Ltd | Construction | 2020 |
| MRJ Limited | Wholesale & retail | 1953 |
| MRS Construction Limited | Construction | 2010 |
| Multiverse Consultants Ltd | Professional & scientific | 2021 |
| Musafit Ltd | Wholesale & retail | 2026 |
| Museum Mews RTM Company Ltd | Households | 2018 |
| Musgrove Ltd | Manufacturing | 2021 |
| Muzlyk Limited | Health & social care | 2021 |
| MVP Health Property Ltd | Real estate | 2024 |
| MW Parking Ltd | Real estate | 2026 |
| My Bookkeepers Ltd | Professional & scientific | 2005 |
| My Concierge London Ltd | Other services | 2024 |
| My Mirror Ltd | Wholesale & retail | 2024 |
| My PA Private Office Limited | Administrative & support | 2019 |
| My Runway Group Ltd | Arts & recreation | 2016 |
| Mywalit (UK) Limited | Wholesale & retail | 2007 |
| N. Forme Limited | Health & social care | 2006 |
| N.J.Shallis Butchers Ltd | Manufacturing | 2011 |
| Naft Investment Limited | Real estate | 2020 |
| Naimlee Limited | Administrative & support | 2017 |
| Nakbat Ltd | Real estate | 2022 |
| Nalathamayanthi & Co Limited | Professional & scientific | 2019 |