| M Kelly Services Limited | Transport & logistics | 2015 |
| M Knight Electrical Limited | Construction | 2021 |
| M L Simpson Repairs Ltd | Wholesale & retail | 2019 |
| M Lynch Security Services Limited | Administrative & support | 2021 |
| M N Furniture Limited | Wholesale & retail | 2019 |
| M Plom Accounting Services Limited | Professional & scientific | 2008 |
| M R S International Limited | Wholesale & retail | 2016 |
| M Scott Interiors Limited | Professional & scientific | 2018 |
| M W Creative Carpentry Limited | Manufacturing | 2021 |
| M Williams Scaffolding Limited | Extraterritorial | 2006 |
| M&A Contracts Ltd | Construction | 2026 |
| M&E Mata Consultancy Ltd | Health & social care | 2020 |
| M&K Sports Ltd | Education | 2025 |
| M&L Property Solutions Ltd | Real estate | 2024 |
| M&L Pycu Limited | Wholesale & retail | 2018 |
| M&M Pro Cleaners Limited | Administrative & support | 2023 |
| M&M Structural & Piling Consultants Limited | Other services | 2018 |
| M&S Motors Trading Limited | Wholesale & retail | 2015 |
| M&V Electrical Ltd | Construction | 2022 |
| M. J. Construct Limited | Construction | 2016 |
| M. Marchant Technical and Design Services Limited | Professional & scientific | 1978 |
| M.A.C Electrical Contracts Ltd | Construction | 2025 |
| M.A.E Electrics Ltd | Construction | 2023 |
| M.A.Trading International UK Ltd | Wholesale & retail | 2023 |
| M.Boost Mobile Aircon & Servicing Ltd | Wholesale & retail | 2026 |
| M.D. Groundworks (South) Ltd | Construction | 2020 |
| M.D. Group (South) Limited | Construction | 2023 |
| M.D. Plant Hire (South) Limited | Construction | 2023 |
| M.Falzon Electrical Contractors Ltd | Construction | 2017 |
| M.Frost Scaffolding Ltd | Construction | 2023 |
| M.I.D. Lighting Limited | Construction | 2001 |
| M.I.T.Construction Ltd | Construction | 2026 |
| M.K Bathrooms Ltd | Wholesale & retail | 2013 |
| M.O.E. Products Ltd | Manufacturing | 2020 |
| M.R.W Electrical & Security Limited | Energy | 2023 |
| M.S.E Managerial Ltd | Professional & scientific | 2015 |
| M.T..Dec.Clean.Ltd Ltd | Other services | 2014 |
| M.Webbers & Sons Ltd | Extraterritorial | 2018 |
| M2-TECH Engineering Services Limited | Professional & scientific | 2024 |
| M2G Facilities Management Ltd | Hospitality | 2021 |
| M3 Events Ltd | Administrative & support | 2026 |
| M8A Ltd | Wholesale & retail | 2025 |
| M8D Investments Ltd | Real estate | 2021 |
| MA Retail Ltd | Wholesale & retail | 2023 |
| Ma.Strum Limited | Manufacturing | 2011 |
| Maall Ltd | Wholesale & retail | 2025 |
| Maas Living Ltd | Wholesale & retail | 2024 |
| MAB Property Group Limited | Real estate | 2026 |
| Macbillion Proptech Ltd | Construction | 2023 |
| Macden Transport Limited | Transport & logistics | 2021 |
| Macgregor Consulting Ltd | Professional & scientific | 2005 |
| Mack (Essex) Ltd | Other services | 2024 |
| Macleod Interiors Limited | Construction | 2019 |
| Macrays Holdings Limited | Professional & scientific | 2018 |
| Macrays Limited | Professional & scientific | 2000 |
| Macs Bar Ltd | Hospitality | 2025 |
| Macs Recruitment Limited | Administrative & support | 2017 |
| Madbellesco Limited | Professional & scientific | 2021 |
| Maddox Consultancy Limited | Professional & scientific | 2013 |
| Maddy MAY Limited | Administrative & support | 2010 |
| Madison's Commercial Solutions Limited | Construction | 2009 |
| Madlen Consultants Ltd | Professional & scientific | 2021 |
| Mads Solutions Ltd | Construction | 2024 |
| MAE Creative Solutions Ltd | Wholesale & retail | 2026 |
| Maea Beauty Ltd | Wholesale & retail | 2021 |
| Maethor Ltd | Professional & scientific | 2025 |
| Magic Basildon Limited | Other services | 2014 |
| Magic HR Limited | Administrative & support | 2025 |
| Magic Look Ltd | Other services | 2020 |
| Magic Shutter Limited | Professional & scientific | 2025 |
| MAGM8 Ltd | Construction | 2024 |
| Magnetar Global Ltd. | Professional & scientific | 2024 |
| Magstickers Ltd | Manufacturing | 2025 |
| MAHADEV8 Ltd | Wholesale & retail | 2023 |
| Mahdeen Construction Limited | Manufacturing | 1998 |
| Mahden Ltd | Hospitality | 2026 |
| Mahdi Group Ltd | Information & communication | 2019 |
| Maheen Healthcare Limited | Health & social care | 2023 |
| Mahi Education Ltd | Administrative & support | 2024 |
| Maia Transport Limited | Transport & logistics | 2021 |
| Main Event Boxing Gym Ltd | Extraterritorial | 2014 |
| Maintaining Matters UK Limited | Administrative & support | 2018 |
| Maintainuk Ltd | Administrative & support | 2015 |
| Maison Beau Investments Ltd | Real estate | 2024 |
| Maiton Limited | Administrative & support | 2014 |
| Majestic Asset Partners Ltd | Real estate | 2026 |
| Majestic Brickwork Limited | Construction | 2016 |
| Majestic Mortgages Ltd | Financial services | 2022 |
| Majestic Shipping International Ltd | Transport & logistics | 2020 |
| Majime Consultancy Ltd | Administrative & support | 2017 |
| Majkut Construction Ltd | Other services | 2025 |
| Make the Headlines Limited | Other services | 2021 |
| Maker & Maker Limited | Professional & scientific | 2016 |
| Maks Desi Delights Ltd | Wholesale & retail | 2025 |
| Malck Limited | Construction | 2025 |
| Malcolm Cooper Consultants Limited | Professional & scientific | 2020 |
| Maldon Fencing and Landscaping Limited | Administrative & support | 2016 |
| Maldon Power Group Ltd | Energy | 2026 |
| Maldon Road Veterinary Practice Limited | Professional & scientific | 2000 |
| Malotti Enterprises Limited | Information & communication | 1990 |