| M.C Arboriculture Ltd | Administrative & support | 2025 |
| M.D. Building and Carpentry Ltd | Construction | 2017 |
| M.E.L. Records Limited | Information & communication | 1995 |
| M.Island Grill Ltd | Hospitality | 2025 |
| M.P. Property Care Ltd | Real estate | 2025 |
| M.R.C. Pension Trust Limited | Financial services | 1975 |
| M.Transporte Ltd | Transport & logistics | 2025 |
| M14 Property Investments Limited | Real estate | 2018 |
| M2CARPATHIAN Ltd | Hospitality | 2021 |
| M3G Estates Limited | Real estate | 2025 |
| M3UYA Limited | Public administration | 2023 |
| M3W Services UK Ltd | Wholesale & retail | 2021 |
| M3W UK Holdings Ltd | Real estate | 2025 |
| M4 Automotive Ltd | Wholesale & retail | 2025 |
| M4 Cars Ltd | Administrative & support | 2017 |
| M4 Lasers Ltd | Manufacturing | 2017 |
| M4 Martt Ltd | Wholesale & retail | 2022 |
| M4 Minibus Centre Limited | Wholesale & retail | 2008 |
| M4 Rescue & Recovery Ltd | Wholesale & retail | 2022 |
| M4 Self Drive Limited | Administrative & support | 2001 |
| M4 Self Drive Trustees Limited | Professional & scientific | 2023 |
| M4 Self Store Limited | Extraterritorial | 2016 |
| M4 Trade Centre Limited | Wholesale & retail | 2008 |
| M4 Van Centre Limited | Wholesale & retail | 2001 |
| MA Tyres Swindon Ltd | Wholesale & retail | 2023 |
| MA UK Logistics Ltd | Wholesale & retail | 2025 |
| MAA Consulting Limited | Information & communication | 2004 |
| Maacoms Ltd | Information & communication | 2013 |
| Maan Prime Estates Ltd | Construction | 2026 |
| Mabel’S Coffee Ltd | Hospitality | 2022 |
| MAC Residential Investments Ltd | Real estate | 2026 |
| Mac's Drylining and Plastering Ltd | Construction | 2015 |
| MAC78 Ltd | Professional & scientific | 2018 |
| Macca's Media Limited | Information & communication | 2024 |
| Maccomforts Ltd | Health & social care | 2026 |
| Macden Limited | Health & social care | 2014 |
| MACG6 Limited | Wholesale & retail | 2023 |
| Mach 3 Studio Ltd | Information & communication | 2025 |
| Mach-Dev Limited | Information & communication | 2022 |
| Machinery Videos Limited | Information & communication | 2020 |
| Macintyre Property Ltd | Real estate | 2025 |
| Mackenzie Solutions Limited | Information & communication | 2012 |
| Mackenzies (Bristol) Limited | Hospitality | 2013 |
| Maclaine Watson & Company Limited | Other services | 1997 |
| Macleod Trading Limited | Wholesale & retail | 2014 |
| Macliff Holdings Ltd | Wholesale & retail | 2022 |
| Macliu Properties Ltd | Administrative & support | 2024 |
| Macnsam Ltd | Wholesale & retail | 2023 |
| Macreation Ltd | Wholesale & retail | 2025 |
| Mactec Installation Ltd | Professional & scientific | 2016 |
| Mactrans PSZ Ltd | Transport & logistics | 2015 |
| MAD Catering Ltd | Hospitality | 2025 |
| Madam Renards Limited | Arts & recreation | 2008 |
| Made by Curious Ltd | Information & communication | 2010 |
| Made by Harriet Limited | Arts & recreation | 2022 |
| Madina Halal Groceries Ltd | Wholesale & retail | 2017 |
| Madras Spices Food Ltd | Hospitality | 2018 |
| Madras Traders Limited | Hospitality | 2025 |
| MAE Networks UK Ltd | Wholesale & retail | 2019 |
| Maftei Drive Ltd | Transport & logistics | 2025 |
| Magdalen Victoria LLP | | 2012 |
| Maggiore Food Ltd | Manufacturing | 2023 |
| Magic Chef (Shirley) Limited | Extraterritorial | 2018 |
| Magic Flame Food Ltd | Hospitality | 2024 |
| Magic Hoops Maidenhead LLP | | 2022 |
| Magic Momo Ltd | Manufacturing | 2020 |
| Magic Touch Promotions Limited | Professional & scientific | 2004 |
| Magnets First Ltd | Manufacturing | 2023 |
| Magno Code Ltd | Professional & scientific | 2021 |
| Magri Holdings Ltd | Real estate | 2025 |
| Mahindra Motors Limited | Wholesale & retail | 2025 |
| Mahiya's Ltd | Wholesale & retail | 2024 |
| Maidment IT Limited | Information & communication | 2010 |
| Maids in Swindon Ltd. | Administrative & support | 2014 |
| Maina Engineering Ltd | Construction | 2024 |
| Maine Holdings 19 Limited | Real estate | 2018 |
| Maintek Limited | Construction | 2003 |
| Maisha Property & Maintenance Ltd | Households | 2023 |
| Maisha Staffing Solutions Ltd | Administrative & support | 2023 |
| Maison & Vacances LET Limited | Construction | 2007 |
| Maiteez Care Ltd | Health & social care | 2015 |
| Majd Contracting Ltd | Construction | 2023 |
| Majda Limited | Transport & logistics | 2011 |
| Majdi Limited | Health & social care | 2013 |
| Majestic Render Ltd | Construction | 2025 |
| Majime Solutions Limited | Professional & scientific | 2018 |
| Majk Development Ltd | Construction | 2021 |
| Majkys Cars Ltd | Wholesale & retail | 2025 |
| Major Visibility Ltd | Information & communication | 2023 |
| Makcom Ltd | Real estate | 2010 |
| Make a Difference Health Care Ltd | Health & social care | 2014 |
| Maketocreate Ltd | Wholesale & retail | 2020 |
| Makeup Clever Ltd | Wholesale & retail | 2022 |
| MAKEUP54 Ltd | Wholesale & retail | 2016 |
| Mako by ME Ltd. | Manufacturing | 2013 |
| Makundi Group Ltd | Financial services | 2025 |
| MAL Building Contractors Ltd | Construction | 2024 |
| Malcolm Corcoran Associates Limited | Manufacturing | 2010 |
| Maldorme Real Estate L.P. | | 2008 |
| Malford Properties Ltd | Construction | 2019 |