| Mckinlay Smith Limited | Other services | 2025 |
| MD King Services Ltd | Administrative & support | 2024 |
| MDA Consultant Limited | Administrative & support | 2001 |
| MDS Services (Cambridge) Ltd | Administrative & support | 2014 |
| Mead Roofing Limited | Construction | 2025 |
| Meadow Lane ST Ives Limited | Extraterritorial | 2019 |
| Meadow Lodge Farm Holidays Ltd | Hospitality | 2026 |
| Meadow View Farm Day Nursery Ltd | Health & social care | 2024 |
| MED4CARE Ltd | Health & social care | 2017 |
| Medallight Limited | Administrative & support | 1992 |
| Medexpress Ltd | Health & social care | 2009 |
| Media Wall Solutions Ltd | Construction | 2025 |
| Medical Assurance Bureau (East Anglia) Limited | Financial services | 2007 |
| Medical Sales Solutions Limited | Professional & scientific | 2025 |
| Medical Sutures Limited | Extraterritorial | 2021 |
| Medicroft Services Ltd | Health & social care | 2020 |
| Medicsauce Consultancy and Healthcare Limited | Health & social care | 2024 |
| Mediprotect Healthcare Limited | Financial services | 2018 |
| Mediumcolinbates Ltd | Education | 2026 |
| Medixrad Limited | Health & social care | 2025 |
| Medjutsu Ltd | Information & communication | 2018 |
| Medklin Limited | Professional & scientific | 2026 |
| Mega Impex Residues Ltd. | Administrative & support | 1997 |
| Megsy Ltd | Wholesale & retail | 2024 |
| Meiling UK Limited | Transport & logistics | 2014 |
| Mejorlo Ltd | Professional & scientific | 2022 |
| Melior Clinics Aesthetic Ltd | Financial services | 2021 |
| Melior Clinics Group Limited | Financial services | 2022 |
| Melior Clinics Limited | Health & social care | 2008 |
| Meliorem Foundation | Professional & scientific | 2023 |
| Mera Mera Ltd | Wholesale & retail | 2026 |
| Mercer Design London Ltd | Wholesale & retail | 2024 |
| Merchant Industrial Supplies Ltd | Wholesale & retail | 2024 |
| Merchant Steel Solutions Ltd. | Construction | 2014 |
| Mereview Taverns Ltd | Hospitality | 2018 |
| Meridian Close Management Company Limited | Households | 2001 |
| Meridian Education Services Limited | Information & communication | 2014 |
| Meridian Trust | Education | 2011 |
| Merlin Bathrooms Ltd | Wholesale & retail | 2012 |
| Merus (UK) Ltd | Administrative & support | 2012 |
| MES Trans Ltd | Transport & logistics | 2021 |
| Mesm Land Strategy Limited | Construction | 2026 |
| Messenger UK Holdco Limited | Administrative & support | 2024 |
| Metal Dwarf Industries Ltd | Arts & recreation | 2010 |
| Metalegs Limited | Manufacturing | 2025 |
| Metrox Taxi Ltd | Transport & logistics | 2025 |
| Mfts Limited | Administrative & support | 2025 |
| MG Bathrooms Ltd | Construction | 2023 |
| MG Construction Services Ltd | Construction | 2024 |
| MG Exotics Limited | Agriculture & fishing | 2025 |
| MG Rushton Limited | Real estate | 2025 |
| MG Total Business Solutions Ltd | Professional & scientific | 2015 |
| MG Yaxley Limited | Real estate | 2025 |
| Mgfm Limited | Construction | 2016 |
| MGM 26 Limited | Information & communication | 2026 |
| Mgpl Property Limited | Real estate | 2016 |
| MGS Brickwork & Developments Ltd | Construction | 2025 |
| MHP Property Holdings Limited | Real estate | 2024 |
| Miafranca Limited | Wholesale & retail | 2020 |
| Miamoree Ltd | Wholesale & retail | 2025 |
| Michael Colmer Plant Hire Limited | Administrative & support | 2006 |
| Michaella Mazzoni Nutrition Limited | Health & social care | 2022 |
| Michelle's Solutions Ltd | Administrative & support | 2025 |
| Mick George Haulage Limited | Extraterritorial | 2022 |
| Microdot Medical Products Limited | Professional & scientific | 2021 |
| Micrologic Design Ltd | Information & communication | 2010 |
| Micron Workholding Limited | Manufacturing | 1994 |
| Microprofessional Limited | Information & communication | 1989 |
| Microsample Ltd | Professional & scientific | 2005 |
| Middlend Consulting Limited | Information & communication | 2002 |
| MIDLIFE360 CIC | Education | 2024 |
| Midloe Farmlink Limited | Agriculture & fishing | 2023 |
| Mike Hathaway Ltd | Professional & scientific | 2011 |
| Mike Private Hire Limited | Transport & logistics | 2023 |
| Mike Westcott Rudd Legal Services Limited | Professional & scientific | 2021 |
| Milburn Holdings Limited | Construction | 2011 |
| Mill Hill Garage (March) Limited | Wholesale & retail | 1974 |
| Mill View Farm Limited | Health & social care | 2014 |
| Miller Telcom Installation Ltd | Information & communication | 2020 |
| Millercraig Investments Ltd | Real estate | 2020 |
| Millfields (Kenninghall) Residents Management Company Limited | Households | 2007 |
| Millie-Helathcare Ltd | Health & social care | 2025 |
| Millinery Malarkey Limited | Manufacturing | 2021 |
| Millington Court Residents Management Company Limited | Households | 1996 |
| Millinson Property Ltd | Real estate | 2026 |
| Million Monkey Software Ltd | Information & communication | 2019 |
| Millwood Private Finance Ltd | Professional & scientific | 2008 |
| Mimeo Limited | Manufacturing | 2000 |
| Mimo's Valeting Service Ltd | Other services | 2015 |
| Mindray (UK) Limited | Wholesale & retail | 2005 |
| Mindvika Limited | Transport & logistics | 2019 |
| Mineheart Limited | Manufacturing | 2012 |
| Mineheart Properties Limited | Real estate | 2019 |
| Mint Motorz Limited | Wholesale & retail | 2018 |
| Mira Software Limited | Information & communication | 2025 |
| Mirabeau Capital LLP | | 2014 |
| Mirabelle Homes Ltd | Real estate | 2021 |
| Miratec Solutions Limited | Information & communication | 2024 |
| Mircea Logistics Ltd | Transport & logistics | 2025 |
| Mirror Finish Cheshire Limited | Administrative & support | 2023 |