| Maskell Group Midlands Limited | Financial services | 2026 |
| Maslow Capital LLP | | 2009 |
| Mason & Co. Financial Planning Ltd | Professional & scientific | 2024 |
| Mason Bradshaw Limited | Professional & scientific | 2011 |
| Mason David Properties Limited | Real estate | 2019 |
| Mason Family Investments Limited | Real estate | 2025 |
| Mason Site Services Limited | Construction | 2011 |
| Mason Woods Ltd | Construction | 2014 |
| Mass Heating Services Ltd | Public administration | 2018 |
| Mass Logistics Ltd | Wholesale & retail | 2012 |
| Masscare Travel and Tours Limited | Administrative & support | 2025 |
| Massco Construction Limited | Construction | 2017 |
| Massco Developments Ltd | Construction | 2021 |
| Massive Protection & Services Ltd | Administrative & support | 2018 |
| Mastac Transport Ltd | Transport & logistics | 2014 |
| Master Autorefinish by Adrianpropainter Ltd | Wholesale & retail | 2025 |
| Master HR Consultancy and Coaching Ltd | Wholesale & retail | 2021 |
| Master Plaster Solutions Ltd | Construction | 2026 |
| Master Relocations Ltd | Transport & logistics | 2020 |
| Mastercladding Ltd | Construction | 2026 |
| Masterful Limited | Hospitality | 2017 |
| Masterloan Limited | Extraterritorial | 2013 |
| Masterminds Tuition Academy Northampton Ltd | Education | 2023 |
| Masterqi Holdings Ltd | Financial services | 2020 |
| Masterqi Ltd | Real estate | 2020 |
| Masters in Travel Ltd | Administrative & support | 2023 |
| Masters Property Lets Ltd | Real estate | 2024 |
| MAT Munn Engineering Ltd | Professional & scientific | 2024 |
| Mata Labs Cosmetics Ltd | Manufacturing | 2018 |
| Matara Foods Limited | Hospitality | 2023 |
| Matavesi Brothers Ltd | Wholesale & retail | 2022 |
| Match 6 Ltd | Professional & scientific | 2023 |
| Matchbox Brewery Ltd | Manufacturing | 2024 |
| Mate Tooling Solutions Limited | Wholesale & retail | 2005 |
| Mate Trans Ltd | Transport & logistics | 2021 |
| Matei &Elena Trans Ltd | Transport & logistics | 2018 |
| Mates Rates Delivery Ltd | Transport & logistics | 2016 |
| Matharu Automotive Limited | Professional & scientific | 2013 |
| Mathew Legal Services Ltd | Professional & scientific | 2020 |
| Mathew Stephen & Co Ltd | Professional & scientific | 2018 |
| Mathieson Assets Limited | Administrative & support | 2015 |
| Mathieson Marble Limited | Wholesale & retail | 1997 |
| Matilda Q Photography Ltd | Professional & scientific | 2020 |
| Matini Montecristo LLP | | 2010 |
| Maton Rose Interiors (UK) Ltd | Professional & scientific | 2011 |
| Matrix Architectural Ironmongery Limited | Wholesale & retail | 2001 |
| Matrix Automations Limited | Information & communication | 2026 |
| Matrix Bar Ltd | Hospitality | 2023 |
| Matrix Diagnostics Limited | Health & social care | 2012 |
| Matrix Haulage Ltd | Transport & logistics | 2026 |
| Matrix Networks (Holdings) Limited | Professional & scientific | 2014 |
| Matrix Networks Group Limited | Financial services | 2018 |
| Matrix Networks Limited | Construction | 2006 |
| Matrix Networks Trustee Limited | Administrative & support | 2018 |
| Matrix Water Limited | Water & waste | 2022 |
| Matt and Summer Property Ltd | Real estate | 2019 |
| Matt Fairgrieve Creative Ltd | Arts & recreation | 2017 |
| Matt Farr Services Ltd | Construction | 2018 |
| Matt Gooding Property Services Limited | Other services | 2019 |
| Matt Newman Film Editing Limited | Information & communication | 2019 |
| Matt Whomes Engineering Limited | Professional & scientific | 2008 |
| Mattacodestudio Ltd | Information & communication | 2023 |
| Mattacola Carpentry Limited | Construction | 2015 |
| Mattacola Property Ltd | Real estate | 2026 |
| Mattan Group Services Ltd | Administrative & support | 2019 |
| Matterhorn Promotions Ltd | Arts & recreation | 2016 |
| Matters of Fact Limited | Professional & scientific | 2001 |
| Mattesth Ltd | Health & social care | 2018 |
| Matthew Fraser Limited | Real estate | 1987 |
| Matthew Hall Electrical Limited | Information & communication | 2015 |
| Matthew Maisey Limited | Wholesale & retail | 2015 |
| Matthew Masters Limited | Wholesale & retail | 2020 |
| Matthew Oliver Windows and Doors Limited | Wholesale & retail | 2013 |
| Matthew Oliver Windows, Doors and Conservatories Limited | Wholesale & retail | 2016 |
| Mattonio Limited | Financial services | 2024 |
| Mattonio Properties Limited | Real estate | 2024 |
| Mattud Ltd | Transport & logistics | 2022 |
| Matumba Ltd | Transport & logistics | 2020 |
| Maturedoffpain Ltd | Wholesale & retail | 2025 |
| MAU Media Ltd | Professional & scientific | 2015 |
| Maulden Residents Management Company Limited | Real estate | 2020 |
| Maule Collective Ltd | Hospitality | 2017 |
| Maureen Boyle Ltd | Professional & scientific | 2011 |
| Maureen Mankaa Ltd | Health & social care | 2025 |
| Maurice Fitch Treeworks Limited | Administrative & support | 2003 |
| Mavani Limited | Professional & scientific | 2010 |
| Maverick Consulting Ltd | Administrative & support | 2022 |
| Maverick Providence Limited | Administrative & support | 2024 |
| Mavino Services Ltd | Information & communication | 2020 |
| Mavis Group Ltd | Construction | 2021 |
| Mavis Technologies Limited | Information & communication | 2023 |
| Mawahid Limited | Wholesale & retail | 2023 |
| Mawsley Day Nursery Limited | Other services | 2009 |
| Mawsley Emergency Vehicle Specialists Ltd | Public administration | 2019 |
| Mawsley Machinery Limited | Wholesale & retail | 1980 |
| Mawsley Trading Co Limited | Information & communication | 2005 |
| MAX & NIK Construct Ltd | Construction | 2026 |
| MAX CAD Tech Design Ltd | Professional & scientific | 2026 |
| MAX Demo Ltd | Construction | 2025 |
| MAX Engel & Co LLP | | 2003 |