| Massey Holdings Limited | Real estate | 2002 |
| Massey PR Limited | Professional & scientific | 2010 |
| Mast Commercial Solutions Ltd | Professional & scientific | 2007 |
| Mast FS Ltd | Financial services | 2009 |
| Mastaflips Ltd | Financial services | 2026 |
| Master Bodyworks Ltd | Wholesale & retail | 2026 |
| Master Cleaners Group Limited | Administrative & support | 2024 |
| Master Elite Fire Ltd | Administrative & support | 2026 |
| Master House United Limited | Administrative & support | 2022 |
| Master Massage Equipment Limited | Wholesale & retail | 2018 |
| Master Sofa Ltd | Wholesale & retail | 2025 |
| Master Sonic Ltd | Transport & logistics | 2019 |
| Masterclass Detailing Limited | Administrative & support | 2020 |
| Masters Academy Bristol LLP | | 2015 |
| Masters Electrical Projects Limited | Construction | 2025 |
| Masters Pipeline Services Limited | Construction | 2003 |
| Masters Roofing Limited | Construction | 2013 |
| Masters Services Limited | Construction | 2025 |
| Mastersofgoods Ltd | Wholesale & retail | 2023 |
| Mastervend Limited | Professional & scientific | 2003 |
| Mastic Works Ltd | Construction | 2019 |
| Masya Ltd | Hospitality | 2018 |
| MAT Mart Limited | Wholesale & retail | 2025 |
| Matar Solar Limited | Energy | 2023 |
| Matcalc Ltd | Information & communication | 2025 |
| Matchbox House Limited | Information & communication | 2018 |
| Matchday Media Group Limited | Information & communication | 2023 |
| Matching Staff Solutions Ltd | Administrative & support | 2018 |
| Matchless Design Ltd | Professional & scientific | 2016 |
| Matchmyadviser Limited | Information & communication | 2025 |
| Matchstick Design & Build Ltd | Real estate | 2005 |
| Mateerenertainment Ltd | Arts & recreation | 2025 |
| Mateoc Limited | Professional & scientific | 2018 |
| Material Earth Limited | Extraterritorial | 2008 |
| Material Exchange Ltd | Wholesale & retail | 2023 |
| Materials in Mind Ltd | Professional & scientific | 2019 |
| Materials Management Limited | Professional & scientific | 2025 |
| Materials Service Group Limited | Professional & scientific | 2024 |
| Materialx Ltd | Information & communication | 2020 |
| Matgast Ltd | Wholesale & retail | 2025 |
| Matha Nineteen Forty Ltd | Wholesale & retail | 2025 |
| Mathembedded Limited | Information & communication | 2009 |
| Matheson Consulting Limited | Financial services | 2014 |
| Mathew.K H Services Limited | Health & social care | 2015 |
| Mathews and Co Limited | Professional & scientific | 2011 |
| Mathias & Sons Ltd | Wholesale & retail | 2001 |
| Mathias Holdings Ltd | Real estate | 2023 |
| Mathias Property Ltd | Real estate | 2024 |
| Mathias Sales Ltd | Wholesale & retail | 2024 |
| Mathias Sourcing Ltd | Real estate | 2025 |
| Mathison Limited | Information & communication | 2021 |
| Matina Middle East Food Limited | Hospitality | 2015 |
| Matinee Properties Ltd | Construction | 2025 |
| Matki Installations Limited | Construction | 2013 |
| Matki Public Limited Company | Manufacturing | 1971 |
| Matraduction Limited | Professional & scientific | 2018 |
| Matrix Accounting and Taxation Solutions Limited | Professional & scientific | 2002 |
| Matrix BES Limited | Construction | 2005 |
| Matrix Capital Investment Co Ltd | Real estate | 2020 |
| Matrix Clinic (Ridgeway) Limited | Health & social care | 2018 |
| Matrix Consultancy Services Limited | Professional & scientific | 2016 |
| Matrix Contract Services Ltd | Construction | 2022 |
| Matrix Demolition Services Ltd | Construction | 2024 |
| Matrix Diamond Drilling Ltd | Construction | 2024 |
| Matrix Lift Services Limited | Manufacturing | 2013 |
| Matrix Office Supplies Ltd | Wholesale & retail | 2008 |
| Matrix Surgical Limited | Health & social care | 2020 |
| Matsource Limited | Administrative & support | 2019 |
| Matsu Digital Limited | Information & communication | 2016 |
| Matt Barrett Ltd | Education | 2024 |
| Matt Dagger Ltd | Construction | 2017 |
| Matt Dodd Coaching Limited | Education | 2024 |
| Matt Gazzard Limited | Wholesale & retail | 2009 |
| Matt George Ltd | Professional & scientific | 2024 |
| Matt Gibson Creative Limited | Administrative & support | 2012 |
| Matt Gray Media Limited | Information & communication | 2002 |
| Matt Hinder Brickwork Ltd | Construction | 2026 |
| Matt Jupe Ltd | Professional & scientific | 2023 |
| Matt Lock Commercials Ltd | Wholesale & retail | 2020 |
| Matt O'Donovan Sculptor Ltd | Arts & recreation | 2016 |
| Matt Richardson Mastic Services Ltd | Construction | 2015 |
| Matt Rudge Limited | Information & communication | 2005 |
| Matt Sweet Ltd | Construction | 2016 |
| Matt Tiltman Ltd | Construction | 2021 |
| Matt Wells Consulting Ltd | Professional & scientific | 2025 |
| Matt Willis Photography Ltd | Extraterritorial | 2017 |
| Matt's Snacks Ltd | Wholesale & retail | 2023 |
| Mattech Limited | Professional & scientific | 2007 |
| Mattem Limited | Real estate | 2013 |
| Matter Limited | Professional & scientific | 2024 |
| Matter of Roots Ltd | Health & social care | 2025 |
| Matter Wholefood Limited | Wholesale & retail | 2015 |
| Matters Magazines Ltd | Information & communication | 2013 |
| Mattertwo Limited | Information & communication | 2023 |
| Mattgoesrogue Ltd | Information & communication | 2025 |
| Matthew Brunning Limited | Professional & scientific | 2015 |
| Matthew Clark Bibendum (Holdings) Limited | Professional & scientific | 2007 |
| Matthew Clark Bibendum Limited | Wholesale & retail | 1990 |
| Matthew Dean Limited | Real estate | 2023 |
| Matthew Gillespie Ltd | Information & communication | 2022 |