| MDI & KO Private Ltd | Transport & logistics | 2025 |
| MDM Europe Ltd | Professional & scientific | 2013 |
| MDT Consultants Limited | Administrative & support | 2010 |
| Meadham Energy Solutions Ltd | Construction | 2020 |
| Meadow Farm (Bedwyn) Management Company Ltd | Households | 2025 |
| Meadow View Bridgerule Residents Company Ltd | Households | 2023 |
| Meakes Energetic Engineering Limited | Professional & scientific | 2013 |
| Meakins Holdings Limited | Financial services | 1998 |
| Meakins Transport Limited | Transport & logistics | 1998 |
| Measys Group Limited | Information & communication | 2015 |
| Medddbase UK Limited | Transport & logistics | 2022 |
| Media Fusion Creative Limited | Administrative & support | 2010 |
| Mediafleet Limited | Professional & scientific | 2003 |
| Medoron Limited | Manufacturing | 2021 |
| Megan Fashion Limited | Wholesale & retail | 2026 |
| Melis (Shrewsbury) Limited | Real estate | 2015 |
| Melville Burbage Holdings Limited | Financial services | 2019 |
| Melville Burbage Insurance Services Limited | Financial services | 2007 |
| Mendip Court Residents Association Limited | Real estate | 1988 |
| Merch Eco Discounts Ltd | Wholesale & retail | 2025 |
| Meridian Cars (Hire) Ltd | Transport & logistics | 2010 |
| Mesi Medical Ltd | Wholesale & retail | 2025 |
| Message Managers Limited | Information & communication | 2012 |
| Messagesphere Limited | Professional & scientific | 2010 |
| Metal in Bloom Ltd. | Manufacturing | 2016 |
| Method Electrical Services Ltd | Construction | 2021 |
| Metis Systems Limited | Information & communication | 2022 |
| Metzger Business Search Ltd | Information & communication | 2007 |
| Metzger Group Limited | Professional & scientific | 2002 |
| Metzger Human Resources Limited | Administrative & support | 2001 |
| Metzger Search & Selection Limited | Administrative & support | 1994 |
| MG Apparel Ltd | Manufacturing | 2025 |
| MG Flats LLP | | 2015 |
| MGA Services Limited | Professional & scientific | 2018 |
| MGC Limited | Information & communication | 1998 |
| MGI Learning Ltd | Education | 2018 |
| MGI Training Ltd | Education | 2018 |
| MGM Motors Koci Ltd | Wholesale & retail | 2024 |
| Miba Sea Home Limited | Real estate | 2022 |
| Michael Cairns Tree Surgery Limited | Administrative & support | 2019 |
| Michael Lawrence Landcrafts Limited | Agriculture & fishing | 2002 |
| Michael Pagliaroli Architects Ltd | Professional & scientific | 2011 |
| Michael Robins Limited | Professional & scientific | 2011 |
| Microdene Limited | Information & communication | 2006 |
| Microflow Enablement Ltd | Professional & scientific | 2026 |
| Micrographica Limited | Administrative & support | 2010 |
| Middlegreen Limited | Real estate | 2003 |
| Midland Access Scaffolding Service Ltd | Construction | 2015 |
| Midwife Beth Limited | Health & social care | 2014 |
| Mielec Solutions Ltd | Wholesale & retail | 2025 |
| Mik's Paints Limited | Wholesale & retail | 2005 |
| Mika Consulting Ltd | Information & communication | 2026 |
| Mike Channon Bloodstock Limited | Agriculture & fishing | 1973 |
| Milan Bancak Limited | Wholesale & retail | 2014 |
| Milbury Commercial Limited | Professional & scientific | 2012 |
| Milbury Contractors Limited | Construction | 2006 |
| Milegate (Newbury) Management Limited | Households | 1992 |
| Milend Ltd | Agriculture & fishing | 2024 |
| Milkhill PIG Company Limited | Agriculture & fishing | 1971 |
| Milkwood Farm Limited | Agriculture & fishing | 2021 |
| Mill Hall Oral School for the Deaf Limited | Education | 1972 |
| Millers Garage (Newbury) Limited | Wholesale & retail | 1998 |
| Millington Hingley Limited | Professional & scientific | 2018 |
| Millyard Ltd | Real estate | 2024 |
| Millymops Cleaning and Maintenance Ltd | Administrative & support | 2017 |
| Milton Technology Services Limited | Professional & scientific | 2004 |
| Mimi’S Kitchen Berkshire Ltd | Manufacturing | 2024 |
| Mimosa Marketing Ltd | Professional & scientific | 2018 |
| Mind Pulse Limited | Information & communication | 2016 |
| Mindflair Games Ltd | Information & communication | 2022 |
| Mini VIE Ltd | Health & social care | 2024 |
| Minim Healthcare Limited | Health & social care | 2008 |
| MIO Fiore Coffee Ltd | Hospitality | 2025 |
| MIO Fiore Ltd | Hospitality | 2015 |
| Mirada Corporate Partners Limited | Financial services | 2017 |
| Misspent Summers Limited | Arts & recreation | 2019 |
| Mistletoe Mews Limited | Construction | 2005 |
| Misuni Holding Limited | Financial services | 2026 |
| Mithila Cultural Society UK C.I.C. | Professional & scientific | 2025 |
| Mitrium Holdings Limited | Financial services | 2016 |
| Mitrium Properties Limited | Real estate | 2018 |
| Miwo Limited | Professional & scientific | 2025 |
| MJ Bikes Limited | Wholesale & retail | 2022 |
| MJD Data Limited | Other services | 2011 |
| MJD Group Services Ltd | Construction | 2020 |
| MJT Pubs Ltd | Hospitality | 2024 |
| MLH Consultants Ltd | Professional & scientific | 2018 |
| MLS Safeguarding and Consultancy Ltd | Education | 2017 |
| Mmce Ltd | Information & communication | 2011 |
| Mmctgroup Limited | Wholesale & retail | 2023 |
| Mmshk Consultants Ltd | Professional & scientific | 2016 |
| MNM International UK Limited | Wholesale & retail | 2017 |
| Mobile UK 21C | Information & communication | 2016 |
| Modbox Spaces (the Park) Limited | Hospitality | 2020 |
| Models for Heroes C.I.C. | Health & social care | 2017 |
| Modla Ltd | Professional & scientific | 2012 |
| Modla PPE Ltd | Manufacturing | 2020 |
| Modus Physiotherapy Limited | Health & social care | 2013 |
| Molly's Fast Food Ltd | Hospitality | 2022 |
| Mollys Express Limited | Hospitality | 2022 |