| M World Business Solutions Limited | Professional & scientific | 2018 |
| M&B S4U Ltd | Transport & logistics | 2022 |
| M&Gp (NO. 1) Ltd | Real estate | 2018 |
| M&Gp (NO. 2) Ltd | Real estate | 2019 |
| M&Gp (NO. 4) Ltd | Real estate | 2020 |
| M&Gp (NO.5) Limited | Real estate | 2024 |
| M&M Engineering Support Ltd | Administrative & support | 2024 |
| M&O Brickwork Services Ltd | Construction | 2023 |
| M.D. Consultancy Services Limited | Information & communication | 2005 |
| M.O.D.L Transport Ltd | Transport & logistics | 2020 |
| M3D4 Property Limited | Real estate | 2021 |
| MA Trading Group Ltd | Wholesale & retail | 2026 |
| MAB Decorating Limited | Construction | 2021 |
| Maciek Cars Ltd | Other services | 2017 |
| Mackenzie Brandt Construction Limited | Construction | 2019 |
| Maclaren Cassells LLP | | 2005 |
| MAD Assets Ltd | Real estate | 2014 |
| MAD Motoring Limited | Wholesale & retail | 2021 |
| Made by Giant Ltd | Information & communication | 2025 |
| Madureira & Cowling Ltd | Hospitality | 2014 |
| MAE Building and Construction Ltd | Construction | 2019 |
| MAE Plant Hire Ltd. | Construction | 2020 |
| Magar Ltd | Transport & logistics | 2018 |
| Magenta Coaching Solutions Limited | Health & social care | 2010 |
| Magic Car Services Ltd | Wholesale & retail | 2019 |
| Magic Gold Ltd | Wholesale & retail | 2024 |
| Magnify & Grow Business Consulting Ltd | Professional & scientific | 2016 |
| Magpas | Health & social care | 2007 |
| Mahove Roof Tiles Ltd | Manufacturing | 2025 |
| Main Logistics Ltd | Transport & logistics | 2022 |
| Mainline Flatpacks Limited | Extraterritorial | 2014 |
| Maison Detre France Limited | Arts & recreation | 2024 |
| Maison Enfant Ltd | Extraterritorial | 2021 |
| Majato Ltd | Real estate | 2024 |
| Makaj & Alex Ltd | Construction | 2020 |
| Make IT Mobile Limited | Professional & scientific | 2013 |
| Makk Healthcare Limited | Health & social care | 2023 |
| Malsencreate Limited | Professional & scientific | 2025 |
| Maltings (Godmanchester) Resident Management Company Limited(The) | Households | 1977 |
| MAN With Tipper Ltd | Water & waste | 2024 |
| MAN With Van Huntingdon Ltd | Transport & logistics | 2013 |
| Manart Limited | Construction | 2006 |
| Manchester Enterprise Limited | Wholesale & retail | 2021 |
| Manchett's Transport Ltd | Transport & logistics | 2021 |
| Manchetts Freight Services Limited | Transport & logistics | 1976 |
| Manciple Limited | Professional & scientific | 2019 |
| Mandlellis Limited | Real estate | 2024 |
| Manley Care Limited | Health & social care | 2010 |
| Mannys Motors Limited | Wholesale & retail | 2022 |
| Manor Courtyard Ltd | Real estate | 2024 |
| Manor Farm (Alconbury) Limited | Agriculture & fishing | 1980 |
| Manor Farm (Brampton) Limited | Health & social care | 2014 |
| Manor Farm Mendip Ltd | Agriculture & fishing | 2022 |
| Manorhouse Architecture Limited | Professional & scientific | 2002 |
| Mansfield Scaffold Store Limited | Wholesale & retail | 2018 |
| Manyco Limited | Financial services | 2023 |
| Maple Research & Development Limited | Professional & scientific | 2018 |
| Mapletoft Ltd | Real estate | 2021 |
| Maraja Estates Ltd | Real estate | 2023 |
| Margaret Walsh Consulting Limited | Professional & scientific | 2008 |
| Maria Kaunert Ltd | Health & social care | 2016 |
| Mariano Cavaleri Limited | Arts & recreation | 2023 |
| Marie Brodie Limited | Health & social care | 2025 |
| Mario Trans&L Ltd | Transport & logistics | 2017 |
| Marivest-Xyz Ltd | Professional & scientific | 2025 |
| Mark RAY Ltd | Financial services | 2005 |
| Mark's Automotive Services Limited | Wholesale & retail | 2016 |
| Markham & George Property Limited | Real estate | 2017 |
| Markham Property Management Ltd | Construction | 2017 |
| Marksman Solutions Ltd | Transport & logistics | 2013 |
| Marley Plastics Limited | Professional & scientific | 1997 |
| Marnik Service Ltd | Other services | 2009 |
| Marquessa Limited | Wholesale & retail | 2008 |
| Marsh Farmer Associates Limited | Administrative & support | 2019 |
| Martan Consultancy Limited | Professional & scientific | 2019 |
| Martens and Prahl International (UK Branch) Limited | Administrative & support | 2025 |
| Martin Taxi Ltd | Transport & logistics | 2023 |
| Martin Thompson Joinery Limited | Construction | 2002 |
| Martin-Jones Technology Limited | Professional & scientific | 2003 |
| Martlet Consulting Group Ltd | Professional & scientific | 2025 |
| Martyn Stewart Electrical Ltd | Construction | 2011 |
| Marutem Limited | Transport & logistics | 2025 |
| Mason&Beck Medical Limited | Health & social care | 2020 |
| Material Property Testing Limited | Professional & scientific | 2022 |
| Maustyns Limited | Professional & scientific | 2018 |
| MAX Cade Limited | Construction | 2016 |
| Maxdram Ltd | Transport & logistics | 2018 |
| Maximegalon Ltd | Information & communication | 2013 |
| Maximus Interior Projects Ltd | Construction | 2026 |
| Maylo Management Ltd | Construction | 2025 |
| Maytrees Enterprises Ltd | Hospitality | 2013 |
| Mayu Trading Ltd | Wholesale & retail | 2021 |
| MAZ Rental Properties Limited | Real estate | 2023 |
| MB Green Flow Solutions Limited | Construction | 2023 |
| MBJ Antwi-Boasiako Ltd | Health & social care | 2024 |
| MC Andrew Investments Limited | Financial services | 2025 |
| Mcauley Holdings Ltd | Real estate | 2019 |
| Mcfarlane Signalling Services Ltd | Manufacturing | 2016 |
| Mcilwain-Grange Limited | Arts & recreation | 2023 |
| Mckie Investments Limited | Real estate | 2023 |