| Marc & Harris Ltd | Wholesale & retail | 2026 |
| Marcel Mediation Letting Ltd | Construction | 2026 |
| Marcel Mediation Ltd | Construction | 2019 |
| Marcell Rail Engineer Limited | Construction | 2019 |
| Marceto Spotcia Ltd | Wholesale & retail | 2026 |
| Marchant Traders Ltd | Wholesale & retail | 2025 |
| Marchbase Limited | Construction | 2012 |
| Marchogion Media Limited | Information & communication | 2005 |
| Marchon Apparel Ltd | Wholesale & retail | 2019 |
| Marchon Athletic Ltd | Arts & recreation | 2016 |
| Marchon Bath Ltd | Arts & recreation | 2024 |
| Marchon Group Ltd | Financial services | 2025 |
| Marchon Gym Group Ltd | Professional & scientific | 2023 |
| Marchon Investments Ltd | Real estate | 2021 |
| Marchon Nutrition Ltd | Extraterritorial | 2020 |
| Marchon Stratford Ltd | Arts & recreation | 2021 |
| Marchon Supplements Ltd | Wholesale & retail | 2022 |
| Marchon Training Ltd | Wholesale & retail | 2019 |
| Marchon Victoria Ltd | Arts & recreation | 2023 |
| Marchynoise Ltd | Information & communication | 2022 |
| Marcin Budzewski Limited | Transport & logistics | 2017 |
| Marco Antônio Ltd | Construction | 2023 |
| Marco DE Carlo Ltd | Manufacturing | 2024 |
| Marcomm Solutions Ltd | Construction | 2019 |
| Mareedcom Ltd | Health & social care | 2019 |
| Marek Trucks Ltd | Transport & logistics | 2025 |
| Marella Cruises Limited | Transport & logistics | 2020 |
| Marfa AL Arabia Limited | Information & communication | 2025 |
| Marfest Care Limited | Health & social care | 2024 |
| Marfil Investments Ltd | Real estate | 2024 |
| Marhal Trans Ltd | Transport & logistics | 2019 |
| Mari Cleaning Limited | Transport & logistics | 2023 |
| Mari J Transport Ltd | Transport & logistics | 2025 |
| Maria Adriano Limited | Construction | 2023 |
| Maria Intizar Fashion Ltd | Wholesale & retail | 2025 |
| Marian Rezz Ltd | Transport & logistics | 2025 |
| Maricosu Dynamics Limited | Real estate | 2025 |
| Maricris Ltd | Construction | 2025 |
| Marilyn Digital Ltd | Wholesale & retail | 2025 |
| Marin Construction Ltd | Construction | 2026 |
| Marina Lebanese Lounge Limited | Hospitality | 2021 |
| Mario Property Maintenance Ltd | Construction | 2020 |
| Mario's Pizzeria Limited | Hospitality | 2014 |
| Mariobamby Ltd | Transport & logistics | 2024 |
| Mariola Kozuszek Nails Academy Ltd | Other services | 2018 |
| Mariomegafam Ltd | Transport & logistics | 2017 |
| Mariotts Legal Services Ltd | Professional & scientific | 2024 |
| Maritza Cleaning Limited | Administrative & support | 2025 |
| Marius Cleaning Specialist Ltd | Construction | 2023 |
| Marius Fibre Ltd | Construction | 2025 |
| Marius Gabriel Lupancu Ltd | Construction | 2016 |
| Marius HGV Trans Ltd | Transport & logistics | 2016 |
| Marius Panait Ltd | Transport & logistics | 2019 |
| MARIUS06 Limited | Administrative & support | 2025 |
| Mariusbartus Ltd | Construction | 2025 |
| Mariusmoldovan Ltd | Transport & logistics | 2025 |
| Marjaans Ltd | Wholesale & retail | 2025 |
| Marjo Transport Ltd | Transport & logistics | 2022 |
| Marjorie's Education Limited | Education | 2018 |
| Marjorie's Education Watford Limited | Education | 2024 |
| Marjorie's Youth Education CIC | Health & social care | 2023 |
| Mark and Chappell Ltd. | Wholesale & retail | 1987 |
| Mark Bowles Limited | Real estate | 2014 |
| Mark Logistics Ltd | Transport & logistics | 2018 |
| Mark Saliba Limited | Health & social care | 2009 |
| Mark Styl Company Ltd | Construction | 2022 |
| Mark's Energy Solutions Ltd | Wholesale & retail | 2020 |
| Markell Luton Limited | Professional & scientific | 1965 |
| Market MAD Limited | Professional & scientific | 2024 |
| Marketing Solutions Group Limited | Professional & scientific | 2017 |
| Marketmax Ltd | Wholesale & retail | 2021 |
| Marketplace MK Limited | Real estate | 2026 |
| Marketvibe Solutions Ltd | Professional & scientific | 2017 |
| Markey Plant Limited | Construction | 2026 |
| Markhor Limited | Wholesale & retail | 2016 |
| Markhor Shield Security Services Limited | Administrative & support | 2021 |
| Markosys Limited | Wholesale & retail | 2024 |
| Markyate Estates LLP | | 2021 |
| Marlborough Automotive Limited | Wholesale & retail | 2025 |
| Marlborough Court Residents (St.Albans) Limited | Real estate | 1991 |
| Marlin Properties Ltd | Real estate | 2021 |
| Marlins Restaurant and Takeaway Ltd | Hospitality | 2025 |
| Marlux Motors Ltd | Wholesale & retail | 2026 |
| Marnbridge Limited | Construction | 1988 |
| Marnova Ltd | Wholesale & retail | 2021 |
| Marock Global Limited | Information & communication | 2024 |
| Maroju & Teki Limited | Health & social care | 2026 |
| Maroon Solutions Ltd | Professional & scientific | 2023 |
| Marra Building Constructions Ltd | Construction | 2025 |
| Marrobwin Ltd | Wholesale & retail | 2025 |
| Marrose Ltd | Households | 2018 |
| Mars Legal Ltd | Administrative & support | 2025 |
| Mars Networks Ltd | Information & communication | 2021 |
| Marsh Construction (Luton) Limited | Construction | 2005 |
| Marsh Engineering & Management Ltd | Other services | 2022 |
| Marsh Farm (Leagrave) Management Company (NO.1.) Limited | Households | 1973 |
| Marsh Farm Futures | Real estate | 2009 |
| Marsh Farm Outreach CIC | Health & social care | 2005 |
| Marsh House Studio Ltd | Education | 2008 |
| Marsh RD Mini Market Ltd | Wholesale & retail | 2024 |