| Martini Car Sales Ltd | Wholesale & retail | 2026 |
| Marvellous School of Motoring Limited | Education | 2025 |
| Marvelwebs Ltd | Information & communication | 2021 |
| Marvillhealthcare Limited | Health & social care | 2018 |
| Marvin Digital Automation Ltd | Information & communication | 2024 |
| Marwa Travels Limited | Administrative & support | 2025 |
| Maryam’S Deals Ltd | Wholesale & retail | 2025 |
| Marykam Limited | Public administration | 2025 |
| Marykess Concept Ltd | Health & social care | 2025 |
| Marynna Ltd | Transport & logistics | 2018 |
| MAS Travel Ltd | Transport & logistics | 2024 |
| MAS Video & Photography Ltd | Professional & scientific | 2021 |
| Mascot Homes Ltd | Construction | 2020 |
| Mase Roofing Ltd | Construction | 2019 |
| Mask Cafe Limited | Hospitality | 2015 |
| Masovia Craft Bakery Ltd | Wholesale & retail | 2026 |
| Mass Medical UK Limited | Manufacturing | 2001 |
| Massey L & P Limited | Real estate | 2016 |
| Masstemps Limited | Administrative & support | 2006 |
| Master Cleaning Supplies Limited | Wholesale & retail | 2016 |
| Master's Tailoring & Fashion Shop Limited | Other services | 2024 |
| Masterkeys Property Ltd | Real estate | 2021 |
| Masters (Home of Snooker) Ltd | Arts & recreation | 2022 |
| Mastrad Furniture Ltd | Wholesale & retail | 2025 |
| Matchaii Limited | Manufacturing | 2025 |
| Matchtag Ltd | Professional & scientific | 2026 |
| Matco Mega Mart Ltd | Hospitality | 2013 |
| Mateo Collections Ltd | Wholesale & retail | 2026 |
| Matford Manufacturing Limited | Manufacturing | 2009 |
| Matford Services Limited | Information & communication | 2011 |
| Math Group Ltd | Wholesale & retail | 2024 |
| Mathews INV Ltd | Real estate | 2021 |
| Matko a Kubko Potraviny Ltd | Hospitality | 2022 |
| Matosche Ltd | Transport & logistics | 2019 |
| Matrix Academy Trust | Education | 2011 |
| Matrix Asset Holdings Limited | Wholesale & retail | 2020 |
| Matrix Code Ltd | Information & communication | 2019 |
| Matrix Doors Ltd | Administrative & support | 2003 |
| Matrix Global Holdings Limited | Financial services | 2020 |
| Matrix Holdings UK Limited | Financial services | 2015 |
| Matrix Online Marketing Ltd | Wholesale & retail | 2024 |
| Matrix Pharmacy Limited | Wholesale & retail | 2003 |
| Matrix Primary Healthcare Ltd | Wholesale & retail | 2007 |
| Matrix Propco Limited | Real estate | 2018 |
| Matt Black Limited | Wholesale & retail | 2020 |
| Matt Black Property Limited | Real estate | 2020 |
| Matt TOM Ltd | Financial services | 2020 |
| Matt Whatton AD Services Ltd | Information & communication | 2024 |
| Mattos Limited | Wholesale & retail | 2020 |
| Mattressshire Limited | Manufacturing | 2009 |
| Mauchak the Honey POT Ltd | Other services | 2017 |
| Maund's Discount Ltd | Wholesale & retail | 2022 |
| MAV Building Limited | Construction | 2024 |
| Maveriol Ltd | Administrative & support | 2024 |
| Mavish Tahir Ltd | Wholesale & retail | 2021 |
| Mavrick Limited | Other services | 2024 |
| Mawand Electricals Limited | Professional & scientific | 2018 |
| Mawes Consulting Ltd | Construction | 2023 |
| Mawillies Care Limited | Public administration | 2025 |
| MAX Davies Limited | Wholesale & retail | 2025 |
| MAX Developing Ltd | Real estate | 2025 |
| Maxim Kamil Zajaczkowski Ltd | Transport & logistics | 2015 |
| Maximus Painting Solutions Ltd | Construction | 2025 |
| Maxjen Group Ltd | Real estate | 2025 |
| Maxjen Haven Cleaning Services Ltd | Administrative & support | 2021 |
| Maxlay K9 Ltd | Administrative & support | 2022 |
| Maxy Tasty Ltd | Hospitality | 2023 |
| Maya 2026 Limited | Real estate | 2025 |
| Maycircle Limited | Health & social care | 2024 |
| Maycroft Residential Properties Ltd | Real estate | 2021 |
| Mayi Trade Inc Ltd | Wholesale & retail | 2022 |
| Maythorn Developments (Horseshoe) Limited | Construction | 2018 |
| Maze Associates Ltd | Other services | 2010 |
| Maze Creative LAB CIC | Education | 2026 |
| Maze Tuition Ltd | Education | 2018 |
| Mazel TOV Services Limited | Administrative & support | 2024 |
| Mazira Limited | Real estate | 2016 |
| Mazz Ltd | Health & social care | 2016 |
| MB & Sons Transport Ltd | Transport & logistics | 2015 |
| MB Food Group Ltd | Manufacturing | 2024 |
| MB Home Builders Ltd | Construction | 2026 |
| MB Implants Limited | Health & social care | 2017 |
| MB Insulation Ltd | Construction | 2024 |
| MB Removal Group Ltd | Transport & logistics | 2024 |
| MB Transport U.K. Ltd | Transport & logistics | 2025 |
| Mbella Care Limited | Health & social care | 2024 |
| Mbes Trading Limited | Wholesale & retail | 2022 |
| MBH Consultancy Limited | Information & communication | 2008 |
| MBH Rental Properties Ltd | Real estate | 2022 |
| MBH Tech Limited | Education | 2025 |
| MBL Realisations Limited | Manufacturing | 1990 |
| MBM Asset Management Ltd | Real estate | 2025 |
| MBM Transport Logistics Limited | Transport & logistics | 2025 |
| Mbsa Ventures Ltd | Real estate | 2025 |
| MC 2025 Realisations Limited | Wholesale & retail | 1979 |
| MC Hvac Solutions Ltd | Professional & scientific | 2022 |
| MC Installations (Midlands) Ltd | Construction | 2021 |
| Mcaleese-Jowett Estate Agents Ltd | Real estate | 2021 |
| Mccall Trading Group Ltd | Professional & scientific | 2019 |
| Mccartney Paint Solutions Ltd | Construction | 2026 |