| Metrikey Limited | Professional & scientific | 2006 |
| Metro Models Ltd | Manufacturing | 2022 |
| Mexican Kitchen Limited | Hospitality | 2018 |
| MF Electrical Solutions Limited | Construction | 2023 |
| MG Aero Engineering Limited | Administrative & support | 2026 |
| MG Affiliates Limited | Professional & scientific | 2013 |
| MG GAS Consultants Ltd | Professional & scientific | 2017 |
| MG the Hair Specialists Limited | Other services | 2022 |
| Mg-Hawkes Ltd | Financial services | 2025 |
| Mgiz Limited | Transport & logistics | 2017 |
| MGK Computing Ltd. | Information & communication | 2024 |
| Mhae Ltd | Arts & recreation | 2025 |
| Michael Frank Limited | Wholesale & retail | 2010 |
| Michael Mcsweeney Associates Limited | Financial services | 2002 |
| Mickie Macie Limited | Construction | 2022 |
| Micky's Catering Company Ltd | Hospitality | 2023 |
| Micro Mold Ltd | Manufacturing | 2020 |
| Middlenorth Management Limited | Real estate | 1993 |
| Mifaloba Ltd | Arts & recreation | 2025 |
| Mike Needham Shipbroking Ltd. | Wholesale & retail | 2003 |
| Miken Limited | Construction | 1988 |
| MIL Interior Ltd | Construction | 2022 |
| Milbourn Electrics Ltd | Construction | 2017 |
| Mill View (ST. Michaels Road) Management Company Limited | Households | 1990 |
| Millane Consulting Ltd | Professional & scientific | 2005 |
| Miller Contracts Ltd | Construction | 2022 |
| Millers Lettings Limited | Real estate | 2024 |
| MIM Therapy Limited | Health & social care | 2020 |
| Minerva Fire & Security Ltd | Administrative & support | 2005 |
| Mingal Ltd | Information & communication | 2021 |
| Minh Chau Limited | Other services | 2024 |
| Mini Vanilla Ltd | Wholesale & retail | 2005 |
| Mipc Ltd | Professional & scientific | 2025 |
| Mirage Display Limited | Professional & scientific | 2012 |
| Mison Consultants Limited | Professional & scientific | 2013 |
| Missspark Ltd | Wholesale & retail | 2013 |
| Mister FIX IT .COM Ltd. | Professional & scientific | 1998 |
| Mister Gees (Property Services) Limited | Construction | 2014 |
| Mister Gees Limited | Real estate | 1993 |
| Mister James Ltd | Education | 2023 |
| Mithra Hamerkops Ltd | Real estate | 2017 |
| MIX Kitchens Ltd | Hospitality | 2023 |
| MIZ Trans Ltd | Transport & logistics | 2019 |
| MJ Joseph Limited | Professional & scientific | 2021 |
| MJ Sevilla Ltd | Health & social care | 2022 |
| MJB Decorating Limited | Construction | 2026 |
| MJD Limited | Construction | 2023 |
| MJG Medic Limited | Health & social care | 2012 |
| MKC Rotor Systems Ltd | Professional & scientific | 2025 |
| Mksb Business Solutions Ltd | Professional & scientific | 2023 |
| Mmcl (Properties) Limited | Real estate | 2016 |
| Mmcl London Ltd | Wholesale & retail | 2021 |
| MMD Developments ( Essex ) Ltd | Wholesale & retail | 2014 |
| MMT Mechanical Ltd | Construction | 2026 |
| Mobile Event Catering UK Ltd | Hospitality | 2015 |
| Mobile Massage & Relax Limited | Extraterritorial | 2023 |
| Modal Leisure Ltd | Hospitality | 2024 |
| Mode Logistics Limited | Transport & logistics | 2009 |
| Modular Cover Systems Ltd | Manufacturing | 2023 |
| Modus Logic Limited | Information & communication | 2012 |
| Molantali Limited | Professional & scientific | 2021 |
| Molybdenum, Tantalum, Tungsten Supplies and Fabrications Ltd | Wholesale & retail | 2008 |
| Mondexa Limited | Administrative & support | 2017 |
| Mondial Engineering Consultancy Limited | Administrative & support | 2008 |
| Mondial Thermography Limited | Professional & scientific | 2011 |
| Monel Limited | Administrative & support | 2014 |
| Monks Building Services Ltd | Construction | 2022 |
| Monolith Roofing and Building Ltd | Construction | 2026 |
| Montcalm Consulting Ltd | Administrative & support | 2020 |
| Moonbeamers Limited | Information & communication | 2015 |
| Moor Top Medical Services Ltd | Administrative & support | 2018 |
| Moore Solutions (AML) Ltd | Administrative & support | 2018 |
| Moore Than Football - Sports Coaching and Mentoring Ltd | Arts & recreation | 2026 |
| Morbec Farm Ltd | Real estate | 2022 |
| Morbio Limited | Financial services | 2012 |
| Morespace Living Limited | Hospitality | 2016 |
| Morgan Alexander Estates Limited | Real estate | 2015 |
| Morgan Alexander Lettings Limited | Real estate | 2018 |
| Morgan Buxton Properties Ltd | Real estate | 2020 |
| Mormont Services Limited | Administrative & support | 2012 |
| Morris & Burgess Ltd | Arts & recreation | 2025 |
| Morris Electrical Solutions Ltd | Construction | 2023 |
| Morris Engineering of Essex Limited | Professional & scientific | 2025 |
| Mother Scrubbers Cleaning Limited | Administrative & support | 2011 |
| Motorised Air Products Limited | Construction | 1989 |
| Motorsport Performance Solutions Limited | Professional & scientific | 2016 |
| Mount Zion Enterprise Ltd | Health & social care | 2013 |
| Mowjo Gardening Services Ltd | Administrative & support | 2021 |
| Mowjo Gardening UK Ltd | Administrative & support | 2022 |
| MP Plumbing & GAS Limited | Construction | 2017 |
| MPB Communications Limited | Information & communication | 2017 |
| MPC Automation Limited | Manufacturing | 2006 |
| MPF Solutions Limited | Construction | 2025 |
| MPR Productions Ltd | Arts & recreation | 2025 |
| Mprop Contractors Limited | Construction | 2025 |
| MR Cosmetics Limited | Wholesale & retail | 2013 |
| MR Stairs Limited | Manufacturing | 2018 |
| Mrkc Ltd | Wholesale & retail | 2024 |
| Mrpc Limited | Professional & scientific | 2025 |
| MS Autocare Ltd | Administrative & support | 2015 |