| Mdmt Consulting Limited | Construction | 2017 |
| MDS Plumbing and Electrics Limited | Construction | 2004 |
| ME Mederos Ltd | Health & social care | 2021 |
| Mead Open Farm Limited | Arts & recreation | 2015 |
| Meadgate Pool Limited | Arts & recreation | 2017 |
| Meadowview Care & Retirement Limited | Professional & scientific | 2023 |
| Meadpath (Chelmsford) Management Company Limited | Households | 1989 |
| Meandros Holdings Ltd | Real estate | 2024 |
| Meantime Promotions Limited | Arts & recreation | 2013 |
| Measuring Machines Limited | Manufacturing | 1927 |
| MEB Dynamics Ltd | Information & communication | 2019 |
| Meca Engineering Ltd | Professional & scientific | 2019 |
| Medhurst Antiques Limited | Wholesale & retail | 2026 |
| Medhurst Estate Management Ltd | Financial services | 2024 |
| Medi Consultancy Ltd | Wholesale & retail | 2021 |
| Medi Sprint Limited | Transport & logistics | 2020 |
| Media Moguls Limited | Administrative & support | 1994 |
| Media Security Systems Limited | Administrative & support | 1997 |
| Media Systems Limited | Information & communication | 1993 |
| MEDIA48 Ltd | Professional & scientific | 2018 |
| Mediakrisuk Limited | Wholesale & retail | 2026 |
| Mediamon Limited | Administrative & support | 2018 |
| Medica 2015 Ltd | Health & social care | 2015 |
| Medical Waste Solutions Limited | Water & waste | 2024 |
| Medicare EMS Group UK Limited | Health & social care | 2006 |
| Medicare EMS Holdings Limited | Financial services | 2024 |
| Medicos-Uk Ltd | Health & social care | 2023 |
| Medipare Limited | Information & communication | 2025 |
| Medivit Ltd | Professional & scientific | 2018 |
| Medlowconsulting Ltd | Professional & scientific | 2016 |
| Medokol Limited | Health & social care | 2016 |
| Medsol Group Limited | Health & social care | 2002 |
| Medsurgica Solutions Limited | Health & social care | 2010 |
| Medway Dermal Fillers Ltd | Other services | 2019 |
| Meetkat TEN Limited | Health & social care | 2023 |
| Megaflatables Limited | Professional & scientific | 2010 |
| Megaflatables Projects Limited | Professional & scientific | 2020 |
| Megamotivation Ltd | Information & communication | 2026 |
| Megance Ltd | Wholesale & retail | 2019 |
| Megathorium Models Ltd | Wholesale & retail | 2024 |
| Megs Bouncy Blowdrys Ltd | Other services | 2026 |
| Meher Psychiatry Ltd | Health & social care | 2025 |
| Mehmil Ltd | Health & social care | 2019 |
| MEK Motors Ltd | Wholesale & retail | 2025 |
| MEL RAE Photogrpahy Limited | Professional & scientific | 2024 |
| Melanin Child Stories Ltd | Wholesale & retail | 2021 |
| Melbourne Park (Chelmsford) Management Company Limited | Households | 1983 |
| Melius People Limited | Professional & scientific | 2017 |
| Melmar Solutions Limited | Professional & scientific | 2024 |
| Melmo Services Limited | Construction | 2025 |
| Melody Match Ltd | Information & communication | 2025 |
| Melrose NW3 Ltd | Arts & recreation | 2023 |
| Melv Sports Holdings Limited | Financial services | 2021 |
| MEM Barber Shop Ltd | Other services | 2025 |
| MEM MEM Ltd | Hospitality | 2025 |
| Mema Car Sales Ltd | Wholesale & retail | 2021 |
| Memento Vivere Ltd | Health & social care | 2026 |
| Memory Making Group Ltd | Wholesale & retail | 2022 |
| MEN of Integrity (MOI) Ltd | Wholesale & retail | 2020 |
| Mend and Heal Ltd | Construction | 2018 |
| Mend Limited | Construction | 2013 |
| Mendis Estates Ltd | Real estate | 2013 |
| Meon Surveyors Ltd | Professional & scientific | 2024 |
| Mepsman Limited | Professional & scientific | 1999 |
| Mera 2017 Ltd | Real estate | 2017 |
| Meraa Properties Limited | Real estate | 2017 |
| Merak Investments Limited | Real estate | 2017 |
| Meraki of London Ltd | Wholesale & retail | 2025 |
| Mercato Imports Ltd | Wholesale & retail | 2026 |
| Merchants Combined Limited | Extraterritorial | 2013 |
| Mercury Leisure Limited | Arts & recreation | 2016 |
| Meridian Soils Limited | Construction | 2000 |
| Merlay Holdings III Limited | Financial services | 2022 |
| Merlay Holdings V Limited | Financial services | 2022 |
| Merlay Holdings VII Limited | Financial services | 2022 |
| Merpitt Payroll and HR Ltd | Professional & scientific | 2024 |
| Merrinworth Limited | Construction | 1987 |
| Mersey Leisure Ltd | Arts & recreation | 2021 |
| Merzario Ltd | Transport & logistics | 2008 |
| Mesame Ltd | Health & social care | 2018 |
| Message Media Limited | Professional & scientific | 2016 |
| Messier 21 Limited | Information & communication | 2018 |
| Metalas (UK) Limited | Manufacturing | 2018 |
| Metalight Limited | Professional & scientific | 2022 |
| Metamorphee Holdings Ltd | Financial services | 2024 |
| Metamorphee UK Ltd | Manufacturing | 2024 |
| Method Contract Services Limited | Construction | 2006 |
| Method IT Services Group Limited | Financial services | 2023 |
| Metric Construction Consultants Ltd | Professional & scientific | 2023 |
| Metropolitan Dog Services Ltd | Administrative & support | 2015 |
| Mettle Works C.I.C. | Arts & recreation | 2025 |
| MEX Technology Ltd | Information & communication | 2025 |
| Mezora Aesthetics Ltd | Health & social care | 2025 |
| MG Arts | Arts & recreation | 2014 |
| MGB Advisory Limited | Professional & scientific | 2026 |
| MGB IT Consulting Limited | Information & communication | 2015 |
| MGC Welding Limited | Construction | 2003 |
| MGD VAT Consultancy Ltd | Professional & scientific | 2014 |
| MGK Seaview Limited | Real estate | 2016 |
| MGR Creation Limited | Professional & scientific | 2024 |