| Mediaz Limited | Wholesale & retail | 2022 |
| Medicaa Limited | Health & social care | 2024 |
| Medical Device Software and Sterilizaiton Professionals Limited | Information & communication | 2016 |
| Medical EA Ltd | Health & social care | 2022 |
| Medical Mortuary Services Ltd | Health & social care | 2019 |
| Medigard UK Ltd | Wholesale & retail | 2024 |
| Medimark International Limited | Professional & scientific | 1995 |
| Mediq Care Ltd | Health & social care | 2021 |
| Medispring Group Ltd | Professional & scientific | 2025 |
| Medprac Ltd | Health & social care | 2023 |
| Mega VR Ltd | Manufacturing | 2023 |
| Megapops Ltd | Health & social care | 2024 |
| Megas Charis Ltd | Real estate | 2024 |
| Meif 7 Tigru Bidco Limited | Financial services | 2022 |
| Meif 7 Tigru Midco Limited | Financial services | 2022 |
| Meili Express Ltd | Transport & logistics | 2022 |
| Melksham Specsavers Limited | Wholesale & retail | 2006 |
| Melksham Visionplus Limited | Wholesale & retail | 2006 |
| Melton Mowbray Specsavers Hearcare Limited | Wholesale & retail | 2017 |
| Melton Mowbray Specsavers Limited | Wholesale & retail | 1994 |
| Melton Mowbray Visionplus Limited | Wholesale & retail | 1994 |
| Melville Rodrigues Consulting LLP | | 2021 |
| Meng & Wing Ltd | Manufacturing | 2023 |
| Meon Associates Ltd | Administrative & support | 2014 |
| Meon Genomics Limited | Information & communication | 2024 |
| Meon Marine Ltd | Agriculture & fishing | 2021 |
| Meon Valley Aggregates Limited | Wholesale & retail | 2012 |
| Meon Valley Butchers Ltd | Wholesale & retail | 2020 |
| Meon Valley HOG Roast Ltd | Hospitality | 2025 |
| Meon Valley Technology Limited | Information & communication | 2006 |
| Meonbridge Limited | Administrative & support | 2019 |
| Meonbrook Limited | Administrative & support | 1995 |
| Meoncorp Limited | Professional & scientific | 2024 |
| Meraki Communications Limited | Information & communication | 2017 |
| Meraki Network Services Limited | Information & communication | 2023 |
| Mercator Media Limited | Information & communication | 1989 |
| Merchant of Magic Limited | Wholesale & retail | 2002 |
| Merdon Investments Limited | Other services | 2013 |
| Mere Green Specsavers Limited | Wholesale & retail | 2016 |
| Meridian Case Management Services Ltd | Health & social care | 2022 |
| Meridian Risk Intelligence Ltd | Information & communication | 2026 |
| Meridian Security Systems Limited | Wholesale & retail | 2004 |
| Meridien Interiors Ltd | Construction | 2013 |
| Merritt Consulting Limited | Professional & scientific | 2025 |
| Merstell Limited | Information & communication | 2025 |
| Merthyr Tydfil 2006 Specsavers Limited | Wholesale & retail | 2005 |
| Merthyr Tydfil 2006 Visionplus Limited | Wholesale & retail | 2005 |
| Merthyr Tydfil Specsavers Hearcare Limited | Wholesale & retail | 2013 |
| MES (Holdings) Limited | Real estate | 2014 |
| Messy Mary Ltd | Hospitality | 2023 |
| MET Fire & Security Limited | Professional & scientific | 2018 |
| Metal Polishing Supplies UK Limited | Wholesale & retail | 1999 |
| Metam Ltd | Hospitality | 2022 |
| Metaxis Training and Consultancy Limited | Education | 2026 |
| Metis Buyco Limited | Financial services | 2023 |
| Metis Topco Limited | Financial services | 2023 |
| Metocean Telematics (U.K.) Limited | Manufacturing | 2017 |
| Mexa Solutions Limited | Administrative & support | 2015 |
| Mexborough Specsavers Limited | Wholesale & retail | 2005 |
| Mexborough Visionplus Limited | Wholesale & retail | 2005 |
| Meyado Private Wealth Management London Ltd | Professional & scientific | 1988 |
| MF NO1 Limited | Construction | 2024 |
| MF NO2 Limited | Construction | 2024 |
| MF NO3 Limited | Construction | 2024 |
| MF NO4 Limited | Construction | 2024 |
| MF NO5 Limited | Construction | 2024 |
| MF NO6 Limited | Construction | 2024 |
| MF NO7 Limited | Construction | 2024 |
| MF NO8 Limited | Construction | 2024 |
| Mgage(Uk) Ltd | Professional & scientific | 2026 |
| MGN Consultancy Limited | Information & communication | 2016 |
| MGV Property Investments Ltd | Real estate | 2025 |
| Mgwc Limited | Professional & scientific | 2018 |
| Mhmts Training Limited | Education | 2005 |
| MI Demolition Consultants Ltd | Professional & scientific | 2022 |
| Micah Consulting Ltd | Professional & scientific | 2011 |
| Michael T. Taylor Decorators Limited | Construction | 2007 |
| Michelle's Swimming Lessons Ltd | Education | 2022 |
| Miconsult Services Ltd | Information & communication | 2023 |
| Micro Dent Laboratory Limited | Manufacturing | 2024 |
| Microdentistry Ltd. | Wholesale & retail | 2014 |
| Microstock (UK) and Sons Limited | Professional & scientific | 2021 |
| Middle Copse Management Company Limited | Households | 2023 |
| Middlebrook Specsavers Limited | Wholesale & retail | 2012 |
| Middlesbrough Specsavers Hearcare Limited | Wholesale & retail | 2005 |
| Middleton Specsavers Hearcare Limited | Wholesale & retail | 2024 |
| Middleton Specsavers Limited | Wholesale & retail | 1994 |
| Middleton Visionplus Limited | Wholesale & retail | 1994 |
| Midlands Regen I GP Limited | Financial services | 2023 |
| Midlands Regen I Limited Partnership | | 2023 |
| Midpoint 27 Management Company Limited | Real estate | 1998 |
| Midsolent Ltd | Professional & scientific | 2024 |
| Midsomer Norton Specsavers Limited | Wholesale & retail | 2017 |
| Midway Sky Ltd | Information & communication | 2012 |
| Mike LEE Limited | Construction | 2012 |
| Mike Richardson Plumbing Ltd | Construction | 2025 |
| Mikes Patisserie Ltd | Hospitality | 2025 |
| Military Clean Services Ltd | Administrative & support | 2022 |
| Milking IT Baby Massage Ltd | Health & social care | 2023 |
| Milking IT Baby Spa and Wellness Ltd | Health & social care | 2023 |