| Maseli Capital Ltd | Financial services | 2026 |
| Mashael Ltd | Education | 2022 |
| Mason Borges Ltd | Financial services | 2025 |
| Mason Commercial Properties Ltd | Real estate | 2018 |
| Mason Finis Limited | Professional & scientific | 2021 |
| Masons Court Management Company (Slough) Limited | Households | 2010 |
| Masroor Health Care Ltd | Health & social care | 2021 |
| Massam Group Ltd | Information & communication | 2026 |
| Mast Investment Management Ltd | Financial services | 2014 |
| Master Designs Essex Ltd | Professional & scientific | 2021 |
| Master Hands Services Ltd | Construction | 2025 |
| Master Products Limited | Manufacturing | 1991 |
| Mastercraft Investment Properties Ltd | Real estate | 2017 |
| Masterframe Limited | Professional & scientific | 2003 |
| Masters Team Cleaning Limited | Administrative & support | 2016 |
| Mastri Ltd | Information & communication | 2024 |
| MAT 3J Limited | Professional & scientific | 2024 |
| Matador Autos LLP | | 2025 |
| Matador Prestige Vehicles Limited | Wholesale & retail | 2020 |
| Matartbet Limited | Professional & scientific | 2025 |
| Material Works Architecture Limited | Professional & scientific | 2017 |
| Mates Mental Health Awareness Through Educational Speaking Community Interest Company | Health & social care | 2019 |
| Matha Supermarket Ltd | Wholesale & retail | 2018 |
| Matlau Ltd | Financial services | 2013 |
| Matra Estates Ltd | Real estate | 2021 |
| Matrix Programme Management Solutions Limited | Information & communication | 2014 |
| Matrix Technology Services Limited | Information & communication | 1997 |
| Matrix Traffic Management Ltd | Transport & logistics | 2024 |
| Matson Martin Holdings Limited | Financial services | 2018 |
| Matt Harrison Photography Limited | Professional & scientific | 2011 |
| Matt James Property Ltd | Real estate | 2020 |
| Matt Knight Ltd | Wholesale & retail | 2018 |
| Matt Wing Photo Ltd | Professional & scientific | 2004 |
| Maude Squared Ltd | Information & communication | 2017 |
| MAV Trans Limited | Transport & logistics | 2023 |
| Mavara House Ltd | Information & communication | 2022 |
| Maven Design and Build Limited | Construction | 2008 |
| Maven Developers Limited | Real estate | 2024 |
| Maverick Consulting Solutions Limited | Professional & scientific | 2010 |
| Maverick Music Limited | Information & communication | 2015 |
| MAX Asbestos Services Limited | Professional & scientific | 2018 |
| MAX Cuthbert Motorsport Limited | Arts & recreation | 2020 |
| Maxilleo Limited | Real estate | 2017 |
| Maximo Scaffolding Limited | Construction | 2022 |
| Maximus Watches Limited | Wholesale & retail | 2011 |
| Maxted - Page Limited | Wholesale & retail | 2002 |
| MAY4IT Solutions Limited | Information & communication | 2012 |
| Maybrick Holdings Limited | Financial services | 2015 |
| Maybrick Inspection & Design Limited | Construction | 2015 |
| Maybrick Limited | Construction | 2001 |
| Maybrick Property Maintenance Limited | Households | 2015 |
| Mayclem Ltd | Health & social care | 2017 |
| Mayde Limited | Arts & recreation | 2009 |
| Mayems Green Limited | Transport & logistics | 2019 |
| Maynabs Ltd | Health & social care | 2022 |
| Mayor Cuttle & Co Ltd | Financial services | 2023 |
| Mays Engineering Ltd | Professional & scientific | 2019 |
| Maze Education Limited | Education | 2015 |
| Mazzini Airco & Solar Ltd | Construction | 2022 |
| MB Consult Services Limited | Professional & scientific | 2024 |
| MB Crane Services Limited | Construction | 2018 |
| MB Heating Engineers Limited | Construction | 2017 |
| Mbeck Consultancy Limited | Professional & scientific | 2025 |
| Mbhhairandbeuty Ltd | Wholesale & retail | 2026 |
| Mbnb Recruitment Ltd | Administrative & support | 2025 |
| Mbrp Ltd | Professional & scientific | 2025 |
| MBS Fitness Limited | Other services | 2025 |
| MBW Accounting Limited | Professional & scientific | 2021 |
| MC Financial Wealth Management Limited | Professional & scientific | 2011 |
| MC Reardon Limited | Financial services | 2023 |
| MC Rigging Ltd | Manufacturing | 2020 |
| Mc&P Services Ltd | Real estate | 2007 |
| MCA Consulting Engineers Limited | Professional & scientific | 1999 |
| Mcavoy Electrics Ltd | Construction | 2024 |
| Mccaig Estimating Ltd | Construction | 2025 |
| Mccarthy Futures and Options Advisory Limited | Financial services | 2019 |
| Mcci Property Ltd | Real estate | 2025 |
| Mcdodd Limited | Arts & recreation | 2024 |
| Mcdonald Highway Services Limited | Construction | 2001 |
| Mcewen Interiors Limited | Construction | 1992 |
| MCF Engineering Resources Ltd | Professional & scientific | 2025 |
| Mcgibbon Engineering Limited | Professional & scientific | 2007 |
| Mcgurk Legal Services Ltd | Professional & scientific | 2025 |
| Mckenna Solutions Limited | Administrative & support | 2024 |
| Mclarens Pure & Natural Limited | Hospitality | 2013 |
| MCM Limelight Limited | Professional & scientific | 2007 |
| Mcmillan Rose & Co Ltd | Professional & scientific | 1997 |
| Mcmillan Rose Accountants Limited | Extraterritorial | 2022 |
| Mcmullon Homes Limited | Construction | 2020 |
| Mcnally Project Management Limited | Construction | 2025 |
| MCO Investments Limited | Real estate | 2015 |
| MCR Express Limited | Wholesale & retail | 2025 |
| MD Plumbing & Building Maintenance Ltd | Construction | 2026 |
| MD Power Services Ltd | Professional & scientific | 2018 |
| Mdach Global Logistics Ltd | Transport & logistics | 2025 |
| MDB Clinical Consultancy Limited | Professional & scientific | 2018 |
| Mdfm Holdings Limited | Financial services | 2011 |
| MDG EN Ltd | Professional & scientific | 2026 |
| MDL Technical & Mechanical Ltd | Wholesale & retail | 2019 |
| MDM Holdings Property Limited | Real estate | 2022 |