| Martin Freeman Ltd | Manufacturing | 2021 |
| Martin Harley Racing Limited | Arts & recreation | 2014 |
| Martin Smith Rigging Services Limited | Information & communication | 2009 |
| Martin Transport Limited | Extraterritorial | 1988 |
| Martin's Builders (Bedford) Ltd | Construction | 2018 |
| Martyn Harper Site Services Limited | Construction | 1999 |
| Marula Contract Services Ltd | Real estate | 2025 |
| Marvellous Minds Tuition Ltd | Education | 2019 |
| Mary Faith Property Group Ltd | Real estate | 2026 |
| Marya Legal Limited | Professional & scientific | 2017 |
| Maryo DRV Services Ltd | Transport & logistics | 2022 |
| Masaco Ltd | Professional & scientific | 2018 |
| Masadaco Limited | Construction | 2019 |
| Masagana Care Limited | Health & social care | 2022 |
| Mash Cars Ltd | Wholesale & retail | 2024 |
| Masha & Co. Limited | Information & communication | 2007 |
| Mashaka Logistics Ltd | Transport & logistics | 2020 |
| Mashoori Marketing Limited | Information & communication | 2017 |
| Masih Electri CAL Services Limited | Construction | 2010 |
| Masih K9 Security Ltd | Administrative & support | 2025 |
| Masih Properties Ltd | Real estate | 2022 |
| Maspash Limited | Health & social care | 2022 |
| Massey Close Residents Association Limited | Households | 1975 |
| Massey Close RTE Company Limited | Real estate | 2010 |
| Massey Construction and Creative Living Limited | Construction | 2022 |
| Massey Services Ltd | Administrative & support | 2017 |
| Massey's Agency (UK) Limited | Administrative & support | 1989 |
| Mast Tech Ltd | Information & communication | 2019 |
| Mastamind Limited | Information & communication | 2023 |
| Master Polish Services Ltd | Wholesale & retail | 2026 |
| Master Sweep (Cornwall) Ltd | Administrative & support | 2016 |
| Masterbt International Ltd | Information & communication | 2016 |
| Mastercoms Limited | Information & communication | 2014 |
| Masterlandscapes Limited | Administrative & support | 2019 |
| Mastroe | Manufacturing | 2009 |
| Masv Limited | Wholesale & retail | 2012 |
| MAT Bircham Electrical Services Limited | Construction | 2012 |
| Mateusz Gumulec Limited | Wholesale & retail | 2016 |
| Mateusz Kuboszek Limited | Wholesale & retail | 2015 |
| Mateusz Prokopczyk Ltd | Wholesale & retail | 2024 |
| Mathewsphotography Ltd | Professional & scientific | 2021 |
| Maths Circle Holdings Limited | Financial services | 2022 |
| Maths Circle Limited | Education | 2015 |
| Maths Paths Limited | Professional & scientific | 2017 |
| Matino Ventures Ltd | Wholesale & retail | 2018 |
| Mato Consulting UK Limited | Other services | 2021 |
| Matra Data Solutions Limited | Information & communication | 2025 |
| Matrix Healthcare Consultancy Ltd | Administrative & support | 2018 |
| Matrix International Limited | Manufacturing | 1998 |
| Matrix Media Ltd | Information & communication | 2013 |
| Matssoft Limited | Professional & scientific | 2013 |
| Matt Barker Coaching and Consulting Ltd | Other services | 2022 |
| Matt Richards OLY Limited | Arts & recreation | 2021 |
| Matt Trapp Technology Consulting Ltd | Information & communication | 2026 |
| Matt's Bar Ltd | Hospitality | 2025 |
| Matterlight Ltd | Wholesale & retail | 2024 |
| Matthew Phillipson Limited | Real estate | 1998 |
| Matthew Trans Ltd | Transport & logistics | 2025 |
| Matthew Welham Building Services Ltd | Construction | 2022 |
| Matthews Privacy Consultancy Ltd | Information & communication | 2022 |
| Matthews Travel and Leisure Group Ltd | Administrative & support | 2021 |
| Mattstone Properties Limited | Real estate | 2020 |
| Mauji Holdings Ltd | Financial services | 2023 |
| Maulden House Consulting Limited | Professional & scientific | 2015 |
| Maulden Mill Limited | Information & communication | 2024 |
| MAW Project Solutions Limited | Professional & scientific | 2024 |
| Mawdsley Properties Ltd | Real estate | 2025 |
| Maxfin Partners Limited | Information & communication | 2013 |
| Maxi Cleaning Services Ltd | Administrative & support | 2023 |
| Maxi Management Ltd | Real estate | 2021 |
| Maxi Pads Ltd | Real estate | 2026 |
| Maxi-Lease INS Solutions Ltd | Wholesale & retail | 2008 |
| Maximum Endorphins Ltd | Arts & recreation | 2021 |
| Maximum Services Limited | Construction | 1991 |
| Maxon Computer Limited | Wholesale & retail | 2000 |
| Maxted & Bareham Financial Services Limited | Financial services | 1998 |
| Maxwell LM Limited | Hospitality | 2026 |
| Maxwell's Hair and Beauty Ltd | Other services | 2005 |
| Maxwells Sales & Marketing Consultancy Limited | Professional & scientific | 2019 |
| MAY Hold Limited | Financial services | 2019 |
| MAY Holdco 1 Limited | Financial services | 2022 |
| MAY XYZ Limited | Agriculture & fishing | 2018 |
| Maya Dusa Limited | Wholesale & retail | 2016 |
| Maya's Cleaning Services Limited | Administrative & support | 2017 |
| Mayes Cafe Ltd | Hospitality | 2023 |
| Mayfair Carpentry Ltd | Manufacturing | 2020 |
| Mayfair Decorating Contractors Limited | Construction | 2011 |
| Mayfair Financial & Mortgage Consultants Limited | Financial services | 2004 |
| Mayfair House Management Services Ltd | Households | 2013 |
| Mayfair Jets UK Ltd | Administrative & support | 2022 |
| Mayfair Properties Beds Ltd | Real estate | 2022 |
| Mayfair Trans Limited | Transport & logistics | 2014 |
| Mayfair Utilities Ltd | Administrative & support | 2016 |
| Mayfield & Wigmore Ltd | Transport & logistics | 2019 |
| Mayfield Business Solutions Limited | Manufacturing | 2012 |
| Mayfield Ventures Ltd | Real estate | 2020 |
| Maylands Estates Limited | Real estate | 2019 |
| Maynard Estate Investments Ltd | Real estate | 2026 |
| Mayokola Healthcare Limited | Health & social care | 2015 |
| Maypond Limited | Professional & scientific | 2000 |