| Mezeray Capital Limited | Real estate | 2025 |
| MFJ Group Ltd | Wholesale & retail | 2021 |
| MG & AJ Homes Ltd | Real estate | 2026 |
| MGA Best Services Ltd | Construction | 2023 |
| MGB Construction Ltd | Construction | 2025 |
| Mgfs Holdings Limited | Financial services | 2026 |
| MGI9 Ltd | Construction | 2026 |
| MGJ Limited | Wholesale & retail | 2023 |
| MGM Brothers Ltd | Construction | 2021 |
| MH (Eastcote Lane Developer) Ltd | Real estate | 2016 |
| MH Builders (Electric & Plumbing) Ltd | Construction | 2023 |
| MH Construction & Stonework Ltd | Construction | 2019 |
| MH Contractors Ltd | Administrative & support | 2025 |
| MH Football World Limited | Education | 2024 |
| MH Plumbing & Heating Solutions Ltd | Construction | 2017 |
| MHF Construction and Engineering Ltd | Construction | 2018 |
| MHRTRADING2 Limited | Wholesale & retail | 2025 |
| Mi:Skin Laser Clinic Limited | Other services | 2019 |
| Miami Local Ltd | Wholesale & retail | 2025 |
| Micasa Rentals Ltd | Real estate | 2022 |
| Michael Belle Consulting Limited | Professional & scientific | 2026 |
| Michael Daniel Consultants Limited | Professional & scientific | 2023 |
| Michael Searle & SON Limited | Manufacturing | 1989 |
| Michael YEO Lettings Limited | Real estate | 2020 |
| Michelle Kaye Training Ltd | Information & communication | 2012 |
| Mickther Limited | Professional & scientific | 2023 |
| Mico Family Ltd | Wholesale & retail | 2023 |
| Micon Global Limited | Administrative & support | 2014 |
| Micro Consulting Limited | Information & communication | 2010 |
| Microfast Ltd | Information & communication | 2017 |
| Microhard Communications Limited | Wholesale & retail | 2020 |
| Microscope Consultants Limited | Professional & scientific | 2021 |
| Micu Daniel Limited | Construction | 2016 |
| Midas Touch Events Limited | Other services | 2012 |
| Middle East Forum Limited | Education | 2025 |
| Middlegame Adventure Limited | Professional & scientific | 2023 |
| Middx Properties Ltd | Real estate | 2015 |
| Mideon Ltd | Construction | 2020 |
| Midland Acquisitions Limited | Other services | 2021 |
| Midsummer Court Limited | Real estate | 2004 |
| Midsummer Management Limited | Households | 2018 |
| Miese Ltd | Professional & scientific | 2026 |
| Migl Construction Ltd | Construction | 2026 |
| Migl Construction Ltd Ltd | Construction | 2026 |
| Mihai Fortis Limited | Construction | 2019 |
| Mike Barton Hypnotherapy Ltd | Health & social care | 2024 |
| Mikorel Limited | Professional & scientific | 2020 |
| Miku Agencies (London) Limited | Wholesale & retail | 1976 |
| Mikumiku Ltd | Real estate | 2024 |
| Milastax Services Ltd | Construction | 2024 |
| Milcot Estates Limited | Real estate | 2024 |
| Milerexx Ltd | Transport & logistics | 2026 |
| Mill Hill Park Cafe Limited | Hospitality | 2023 |
| Millennium Urban Films Ltd | Information & communication | 2022 |
| Milsona Limited | Real estate | 2020 |
| Milton Keynes Dental Clinic Limited | Health & social care | 2017 |
| Milvian Facilities Ltd | Construction | 2026 |
| Mimi Autopsy Services Limited | Health & social care | 2021 |
| Mimi&You Limited | Wholesale & retail | 2014 |
| MIN Website Service Limited | Other services | 2023 |
| Mina BAG Limited | Other services | 2025 |
| Minat Ltd | Wholesale & retail | 2015 |
| Mind Move Limited | Education | 2023 |
| Mindeva Property Limited | Real estate | 2018 |
| Mine 24/7 Limited | Health & social care | 2018 |
| Minimi Ltd | Wholesale & retail | 2016 |
| Minky MOO Productions Limited | Information & communication | 2014 |
| Mirage Developments Limited | Real estate | 2000 |
| Mirage Lite Ltd | Construction | 2025 |
| Mirage Motor Sport Limited | Arts & recreation | 1992 |
| Mirevy Ltd | Health & social care | 2025 |
| Miri Estates Ltd | Real estate | 2022 |
| Mirroredbyarnelle Limited | Other services | 2024 |
| Mirzai London Ltd | Wholesale & retail | 2025 |
| Mish Assets Ltd | Real estate | 2021 |
| Mishi Goods Ltd | Administrative & support | 2012 |
| Misocat Ltd | Information & communication | 2025 |
| Miss Nigeria UK Limited | Information & communication | 2010 |
| Missenden Property Services Ltd | Real estate | 2020 |
| Mitchell Brook Gardens NO.3 Residents Company Limited | Households | 1993 |
| Miter Electrical Ltd | Construction | 2019 |
| Mithila Homes Private Limited | Real estate | 2019 |
| Mithra's Enterprises Ltd | Wholesale & retail | 2022 |
| Mithra's Retail Ltd | Wholesale & retail | 2025 |
| Mithras Construction Management Ltd | Construction | 2019 |
| Mitica Ltd | Construction | 2014 |
| Mitteloupe Limited | Professional & scientific | 2014 |
| Miva Consultancy Ltd | Professional & scientific | 2022 |
| Miworld Limited | Information & communication | 2004 |
| Mixed Source Limited | Wholesale & retail | 2022 |
| MJ Import Ltd | Wholesale & retail | 2025 |
| MJ Infrastructure Ltd | Construction | 2026 |
| MJ Sons Limited | Wholesale & retail | 2023 |
| MJA Health Limited | Health & social care | 2012 |
| MJB Medical Ltd | Health & social care | 2022 |
| MJH Medical Limited | Health & social care | 2010 |
| MJH Safety Solutions Limited | Professional & scientific | 2010 |
| MJM Mart Limited | Wholesale & retail | 2026 |
| Mjrb Ltd | Real estate | 2024 |
| MJS Digital Limited | Information & communication | 2019 |