| Lytek Limited | Real estate | 2016 |
| M & J Communications Limited | Information & communication | 1996 |
| M Cooper Holdings Ltd | Real estate | 2025 |
| M Cubed Building Services Ltd | Construction | 2021 |
| M J Property Lettings Ltd | Real estate | 2023 |
| M J R Drylining Contractors Limited | Construction | 1997 |
| M J R Property Investments Limited | Real estate | 2020 |
| M JAR Lounge Ltd | Other services | 2019 |
| M K Hair Loss Clinic Limited | Other services | 2024 |
| M Payne Consulting Ltd | Professional & scientific | 2023 |
| M S General Builders Ltd | Construction | 2016 |
| M&F Tree Care Ltd | Administrative & support | 2025 |
| M&V Baby Sensory Limited | Administrative & support | 2015 |
| M-Theory Creative Limited | Information & communication | 2018 |
| M2M Pharmaceuticals Ltd | Professional & scientific | 2016 |
| M3 Property Management Limited | Wholesale & retail | 2025 |
| MAA Residential Ltd | Real estate | 2024 |
| MAA Sharada Properties Ltd | Real estate | 2024 |
| Machinemove Limited | Construction | 2009 |
| Made for People Ltd | Information & communication | 2024 |
| Madhan Property Services Ltd | Real estate | 2017 |
| Madhan's AM 2 PM Limited | Wholesale & retail | 2013 |
| Magal Bond Properties Limited | Real estate | 2017 |
| Magic Cuts Wokingham Ltd | Other services | 2025 |
| Magic HCW Ltd | Other services | 2017 |
| Magic Hoops Birmingham LLP | | 2023 |
| Magic Hoops Limited | Arts & recreation | 2021 |
| Magick EYE Records Limited | Information & communication | 1991 |
| Magna Consulting Services Limited | Administrative & support | 2014 |
| Magna DEV Solutions Ltd | Information & communication | 2011 |
| MAH Commerce Limited | Manufacturing | 2020 |
| Mai-Dei Limited | Health & social care | 2018 |
| Maidenhead Altwood Astro Limited | Other services | 1992 |
| Maidenhead Basketball Academy Limited | Arts & recreation | 2020 |
| Mail Order Herbs Ltd | Wholesale & retail | 2023 |
| Mailcms Limited | Information & communication | 2025 |
| Maintenance and Keyholding Fran Salar Ltd | Administrative & support | 2019 |
| Maison Estate Agency Limited | Real estate | 2024 |
| Maison Rustic Ltd | Wholesale & retail | 2019 |
| Maiva Clearance Solutions Ltd | Transport & logistics | 2024 |
| Maiva Eco Ltd | Construction | 2025 |
| Maiva Property Solutions Ltd | Households | 2020 |
| Maiva Roofing Limited | Construction | 2018 |
| Majerro Corp Limited | Professional & scientific | 2024 |
| Majestic Impact Advertising Limited | Administrative & support | 2012 |
| Major Landscapes Ltd | Construction | 2018 |
| Make Engineering Design Limited | Manufacturing | 2023 |
| Make-Up Your Mind (MYM) Ltd | Wholesale & retail | 2020 |
| Making Records Simple Limited | Administrative & support | 2015 |
| Makous Ventures Ltd | Professional & scientific | 2025 |
| Makrosoft Limited | Information & communication | 2015 |
| Malafit Ltd | Wholesale & retail | 2026 |
| Malbec Bidco Limited | Financial services | 2024 |
| Malbec Midco Limited | Financial services | 2024 |
| Malbec Topco Limited | Financial services | 2024 |
| Malhan Consulting Limited | Professional & scientific | 2023 |
| Malikbrothersawan Ltd | Wholesale & retail | 2025 |
| Malinkey Biomedical Solutions Ltd | Professional & scientific | 2026 |
| Mallabar Limited | Wholesale & retail | 1998 |
| Malvern House Estate Management Company Limited | Households | 1966 |
| Mambo Leisure Masters Limited | Administrative & support | 2023 |
| Mangal Turkish Grill Ltd | Hospitality | 2024 |
| Manhattan Associates Limited | Information & communication | 1998 |
| Manning Heights Limited | Real estate | 2021 |
| Manon ET Jacob Limited | Arts & recreation | 2022 |
| Manor Barns Residents Company Limited | Real estate | 2005 |
| Manor House Residents Association (Camberley) Limited(The) | Households | 1982 |
| Mantegro Ltd | Transport & logistics | 2022 |
| Manthan Ltd | Wholesale & retail | 2023 |
| Mantichore Ltd | Health & social care | 2021 |
| Mantle Limited | Other services | 2000 |
| Manzeeproperties Ltd | Real estate | 2026 |
| MAO Ltd | Professional & scientific | 2012 |
| Marbaysu Health Limited | Health & social care | 2022 |
| Marc the Dent MAN Ltd | Wholesale & retail | 2006 |
| Marchthyme Property Management Limited | Households | 2003 |
| Marco Island Ltd | Administrative & support | 2006 |
| Marco Pietro Limited | Wholesale & retail | 2025 |
| Mardlin Consulting Limited | Administrative & support | 2025 |
| Margaret Homes Limited | Health & social care | 1977 |
| Mariborne Property Management Limited | Real estate | 2023 |
| Maritime Gaming Ltd | Arts & recreation | 2023 |
| Mark Allen Cars Ltd | Extraterritorial | 2003 |
| Mark Ayres Training and Consultancy Limited | Wholesale & retail | 2014 |
| Mark DEN Haring Lewis Ltd | Information & communication | 2003 |
| Mark Palmer Ltd | Arts & recreation | 2022 |
| Mark Windle Limited | Professional & scientific | 2014 |
| Markel Services Ltd | Information & communication | 2019 |
| Marketabl Ltd | Professional & scientific | 2025 |
| Marketing and Sales Solutions Limited | Professional & scientific | 2009 |
| Marketing Boost Limited | Professional & scientific | 2011 |
| Markham Consultancy Ltd | Professional & scientific | 2026 |
| Marln Group Ltd | Professional & scientific | 2021 |
| Marlow Communications Limited | Information & communication | 1997 |
| Marmic Team Limited | Construction | 2016 |
| Maro Digital Limited | Professional & scientific | 2023 |
| Marr Investments Ltd | Real estate | 2019 |
| Marr Properties Limited | Real estate | 1988 |
| Marshall Roofing and Building Services Ltd | Construction | 2026 |
| Marthews Limited | Professional & scientific | 2013 |