| Mario's Pizza'Z Limited | Hospitality | 2026 |
| Marios Kirkgate Limited | Other services | 2015 |
| Marios Wool Exchange Limited | Other services | 2015 |
| Marius Builders Ltd | Construction | 2023 |
| Marjan Courier Limited | Transport & logistics | 2023 |
| Mark Bullivant Ltd | Transport & logistics | 2025 |
| Mark Hotte (Roofing) Ltd | Construction | 2023 |
| Mark LEE Racing Ltd | Arts & recreation | 2019 |
| Mark LEE Transport Limited | Transport & logistics | 2011 |
| Mark O'Brien Buildings Limited | Real estate | 1983 |
| Mark Pick Limited | Construction | 2019 |
| Mark's Auto Care Garage Ltd | Wholesale & retail | 2023 |
| Market Bidco Finco PLC | Financial services | 2021 |
| Market Bidco Limited | Financial services | 2021 |
| Market Holdco 1 Limited | Financial services | 2021 |
| Market Holdco 2 Limited | Financial services | 2021 |
| Market Holdco 3 Limited | Financial services | 2021 |
| Market Holdco Grpc 1 LLP | | 2023 |
| Market Holdco Grpc 2 LLP | | 2023 |
| Market Holdco Grpc 3 LLP | | 2023 |
| Market Holdco Grpc 4 LLP | | 2024 |
| Market Holdco Grpc Member 1 Limited | Financial services | 2023 |
| Market Holdco Grpc Member 2 Limited | Financial services | 2023 |
| Market Holdco Grpc Member 3 Limited | Financial services | 2024 |
| Market Holdco Grpc Member 4 Limited | Financial services | 2024 |
| Market Parent Finco PLC | Financial services | 2021 |
| Market Street Fish & Chips Ltd | Hospitality | 2025 |
| Market Tavern Wibsey Ltd | Hospitality | 2022 |
| Market Topco Limited | Financial services | 2021 |
| Marketplace Leisure Ltd | Hospitality | 2020 |
| Markex Consulting Ltd | Professional & scientific | 2025 |
| Markhor Handicrafts Ltd | Wholesale & retail | 2021 |
| Markola Limited | Professional & scientific | 2021 |
| Marksman Construction Ltd | Construction | 2022 |
| Marlborough Pitstop MOT Centre Ltd | Wholesale & retail | 2023 |
| Marlborough Rentals Limited | Information & communication | 1980 |
| Marmita Group Limited | Hospitality | 2025 |
| Marnie Millard Limited | Professional & scientific | 2020 |
| Marose Aesthetics Ltd | Other services | 2023 |
| Marque of Brands Limited | Wholesale & retail | 2015 |
| Marquee Moments Ltd | Professional & scientific | 2025 |
| Marquis Private Hire Ltd | Transport & logistics | 2026 |
| Marrs Capital Investments Limited | Real estate | 2025 |
| Marrs Care Limited | Financial services | 2017 |
| Marsh Food Store Limited | Wholesale & retail | 2024 |
| Marsh Projects Ltd | Construction | 2020 |
| Marshall & Craven Limited | Manufacturing | 2010 |
| Marshall Conversions Ltd | Construction | 2020 |
| Marshalls Bakehouse Limited | Manufacturing | 2023 |
| Marshfield Stores BD Ltd | Wholesale & retail | 2024 |
| Marstair Limited | Extraterritorial | 2003 |
| Marsylka Holdings Limited | Financial services | 2023 |
| Marsylka Manufacturing Co.Limited | Manufacturing | 1946 |
| Martenspeed Ltd | Transport & logistics | 2025 |
| Martin Birkbeck Limited | Construction | 2026 |
| Martin Garside Limited | Construction | 2008 |
| Martin Lonsdale Estates Limited | Real estate | 2005 |
| Martin Plumbing Ltd | Construction | 2025 |
| Martin Renovation Services Limited | Construction | 2017 |
| Martin's Logistics Ltd | Transport & logistics | 2025 |
| Martins Gross Ltd | Transport & logistics | 2018 |
| Marvah Rana Ltd | Professional & scientific | 2021 |
| Marvel Payroll Limited | Construction | 2015 |
| Marvellous Souls Care Services Ltd | Health & social care | 2025 |
| Marvelpower Ltd | Transport & logistics | 2025 |
| Marvis Mark Ltd | Professional & scientific | 2026 |
| Marvyko Ltd | Wholesale & retail | 2021 |
| Marwaha Estate Ltd | Real estate | 2017 |
| Mary Magdalene CIC | Health & social care | 2016 |
| Mary Street Windows Limited | Manufacturing | 2023 |
| Marya Ltd | Construction | 2025 |
| Maryam & Mariya's Ltd | Wholesale & retail | 2024 |
| Maryam Faisal Bridal Studio Ltd | Wholesale & retail | 2018 |
| Maryam Faisal Pret-A- Porter Ltd | Wholesale & retail | 2021 |
| Maryna (Private) Ltd | Extraterritorial | 2014 |
| Maryna Financial Ltd | Real estate | 2014 |
| Marzi AY Ltd | Wholesale & retail | 2025 |
| MAS Builders Warehouse Ltd | Construction | 2022 |
| MAS Clinical Solutions Ltd | Health & social care | 2025 |
| MAS Global Group Ltd | Health & social care | 2025 |
| MAS Telecommunication Services Ltd | Information & communication | 2023 |
| MAS Universal Ltd | Construction | 2024 |
| Mas&A Properties Ltd | Real estate | 2025 |
| Masahar Ltd | Health & social care | 2021 |
| Masalam Thornton Ltd | Hospitality | 2023 |
| Masaun Property Ltd | Real estate | 2022 |
| Mascon Ltd | Education | 2024 |
| Masd Development Limited | Construction | 2020 |
| Masdent Ltd | Health & social care | 2020 |
| Maser Limited | Other services | 2014 |
| Masg Transport Ltd | Transport & logistics | 2020 |
| Mashal Technologies Limited | Wholesale & retail | 2026 |
| Masham Homes Ltd. | Construction | 2014 |
| Mashreq Boutique Limited | Wholesale & retail | 2026 |
| Mashriq Events Limited | Administrative & support | 2021 |
| Mashriq Occasions Limited | Administrative & support | 2017 |
| Maskan Properties Limited | Real estate | 2017 |
| Masofology Ltd | Other services | 2023 |
| Mason Collectibles Ltd | Wholesale & retail | 2021 |
| Masons Egerton Ltd | Hospitality | 2023 |