| Melio Medical Limited | Manufacturing | 2017 |
| Meller Speakman (Infrastructure) Limited | Professional & scientific | 2022 |
| Meller Speakman (Sales) Limited | Real estate | 2025 |
| Meller Speakman Holdings Limited | Financial services | 2016 |
| Meller Speakman Limited | Real estate | 2016 |
| Melmade Ltd | Administrative & support | 2016 |
| Mens Vitality Limited | Information & communication | 2016 |
| Mentr Limited | Information & communication | 2025 |
| MEP4 Offsite Limited | Construction | 2022 |
| MER Williamson Limited | Health & social care | 2016 |
| Merchifi Limited | Wholesale & retail | 2018 |
| Mere Home Farm Management Company Limited | Households | 2006 |
| Merlin Oak Ltd | Real estate | 2024 |
| Merlyn Industries U.K. Limited | Wholesale & retail | 2000 |
| Merovingii Ltd | Real estate | 2018 |
| Metabexa Limited | Professional & scientific | 2025 |
| Metis Flooring Ltd | Administrative & support | 2012 |
| Metlex Industries Limited | Professional & scientific | 1986 |
| Metrophase Limited | Information & communication | 2014 |
| Meulensteen Media Limited | Information & communication | 2024 |
| MEX Eco Products Ltd | Construction | 2019 |
| Meze Greek Restaurant Ltd | Hospitality | 2022 |
| MF Finance Consulting Ltd | Professional & scientific | 2026 |
| Mfitness Limited | Professional & scientific | 2013 |
| MG Anaesthetics Limited | Health & social care | 2026 |
| MGB Consultants Ltd | Information & communication | 2026 |
| MGS Neurology Limited | Health & social care | 2023 |
| Mhad Co Limited | Other services | 2024 |
| MHR Dental Ltd | Health & social care | 2013 |
| MHT Specialist Ltd | Professional & scientific | 2022 |
| MI Lash Pro Limited | Other services | 2020 |
| Micare Limited | Real estate | 2019 |
| Michael Brown Properties Ltd | Real estate | 2005 |
| Michael Gaunt Limited | Health & social care | 2012 |
| Michael J Chapman Estate Agents Limited | Real estate | 2009 |
| Michael James Kenyon Ltd | Professional & scientific | 2012 |
| Michael O'Neill Contracting Ltd | Professional & scientific | 2010 |
| Michelle Pamment Communications Limited | Professional & scientific | 2015 |
| Mick Mann Ltd | Information & communication | 2025 |
| Micromass Holdings Limited | Professional & scientific | 2000 |
| Micromass Limited | Professional & scientific | 1995 |
| Micromass UK Limited | Manufacturing | 1996 |
| Microton Technology Limited | Wholesale & retail | 2006 |
| Microtron International Ltd | Manufacturing | 2010 |
| Middle East Legal Consultant Office Ltd | Professional & scientific | 2024 |
| Midland Precision Equipment Co. Limited | Manufacturing | 1941 |
| Midland Safety Management Ltd | Professional & scientific | 2006 |
| Midlands Heartbeat LLP | | 2023 |
| Midlandsecho Ltd | Health & social care | 2020 |
| Mike Hayton Limited | Health & social care | 2011 |
| Mila's Cafe Ltd | Hospitality | 2021 |
| Miles Beyond Ltd | Wholesale & retail | 2024 |
| Milford Anaesthesia Limited | Health & social care | 2022 |
| Mill Brow Cricket Flour Limited | Professional & scientific | 2018 |
| Mill Lodge (Boston) RTM Company Limited | Households | 2022 |
| Miller Surgical Limited | Health & social care | 2013 |
| Millers Place (Bedford) Management Company Limited | Households | 2014 |
| Millington & Millington Limited | Health & social care | 2014 |
| Milta Pharmaceuticals Ltd | Health & social care | 2021 |
| Mil’S ( Wilmslow ) Ltd | Hospitality | 2023 |
| Mind Matters Consulting Limited | Administrative & support | 2009 |
| Minerva Green Growth Property Limited Partnership | | 2010 |
| Mini Investments 2023 Limited | Financial services | 2023 |
| Mini Padel Ltd | Education | 2025 |
| Minisports Coaching Limited | Education | 2018 |
| Minisports Macclesfield, Congleton, Buxton & Leek Ltd | Arts & recreation | 2025 |
| Minnova Medical Foundation C.I.C. | Other services | 2017 |
| Mint Productions London Limited | Administrative & support | 2010 |
| Mirrorball Limited | Professional & scientific | 1999 |
| Mirth Construction Ltd | Professional & scientific | 2021 |
| Mis-Sold.Com Limited | Professional & scientific | 2025 |
| Misha Medical Limited | Real estate | 2017 |
| Misshapen Ventures Ltd | Professional & scientific | 2025 |
| Mistral (UK) Ltd | Real estate | 2011 |
| Miura Real Estate Advisors Limited | Real estate | 2024 |
| Mixsoon UK Ltd | Wholesale & retail | 2025 |
| MJ Regan Properties Limited | Real estate | 2014 |
| MJ Software Services Limited | Professional & scientific | 2021 |
| MJF Facilities Management Limited | Administrative & support | 2015 |
| MJG Medical Limited | Health & social care | 2022 |
| Mjlr Holdings Ltd | Financial services | 2025 |
| MJT Health Limited | Health & social care | 2025 |
| MK Group Incorporated Ltd | Financial services | 2020 |
| MK Plant Rentals Limited | Administrative & support | 2025 |
| MK Residential Developments Limited | Construction | 2019 |
| MK Trading Services Ltd | Wholesale & retail | 2018 |
| Mklindop Limited | Information & communication | 2014 |
| MKM North West Ltd | Administrative & support | 2021 |
| MKR Media Ltd | Professional & scientific | 2015 |
| Mksl Holdings Limited | Real estate | 2024 |
| ML Hospitality (Atherton) Ltd | Hospitality | 2025 |
| ML Plastering & Renovations Ltd | Construction | 2019 |
| ML Trading Ltd | Wholesale & retail | 2025 |
| Mlab Manchester Ltd | Other services | 2021 |
| MLC Financial Services Ltd | Financial services | 2018 |
| Mldr Ltd | Real estate | 2025 |
| MLJ Capital Limited | Financial services | 2026 |
| MM Construction Engineering Ltd | Professional & scientific | 2016 |
| Mmdg Consulting Limited | Professional & scientific | 2019 |
| MMH Group Limited | Financial services | 2025 |