| Market Road Management Company Limited | Professional & scientific | 1994 |
| Market Swipe Technologies Limited | Wholesale & retail | 2024 |
| Market TTL Ltd | Information & communication | 2014 |
| Marketina Ltd | Professional & scientific | 2025 |
| Marketing & Creative Solutions Limited | Wholesale & retail | 1986 |
| Marketing 4 Contractors Ltd | Administrative & support | 2015 |
| Marketing Analysis & Consultancy Limited | Professional & scientific | 2020 |
| Marketing and Commerce Limited | Manufacturing | 2025 |
| Marketing by MJA Limited | Administrative & support | 2014 |
| Marketing Funnels Media Ltd | Professional & scientific | 2019 |
| Marketing Gorillaz Ltd | Wholesale & retail | 2024 |
| Marketing Initiatives Limited | Wholesale & retail | 2003 |
| Marketing Supplies Limited | Information & communication | 2014 |
| Marketingnow Ltd | Other services | 2025 |
| Marketingwithcameron.Com Ltd | Professional & scientific | 2025 |
| Marketlogic Labs Limited | Professional & scientific | 2025 |
| Marketoro Limited | Information & communication | 2025 |
| Marketplace Unlimited UK Ltd | Wholesale & retail | 2023 |
| Marketra Ltd | Professional & scientific | 2026 |
| Markets ETC Ltd | Information & communication | 2016 |
| Markets Mosaic Ltd | Information & communication | 2025 |
| Marketspace Limited | Wholesale & retail | 1999 |
| Markfern Limited | Professional & scientific | 2018 |
| Markle Engineering Limited | Manufacturing | 2019 |
| Markload Services Ltd | Manufacturing | 2019 |
| Markmac Ltd | Other services | 2019 |
| Marko Anstice Limited | Professional & scientific | 2019 |
| Marko Services Ltd | Information & communication | 2025 |
| Marks Online Services Ltd | Administrative & support | 2025 |
| Marksman Global Limited | Wholesale & retail | 2025 |
| Markstein Erdbau UND Transport Limited | Extraterritorial | 2013 |
| Markston Limited | Extraterritorial | 2000 |
| Marky Trading Ltd | Transport & logistics | 2020 |
| Marlboro (UK) Industrial Limited | Extraterritorial | 2019 |
| Marlborough Freehold Limited | Households | 2021 |
| Marlene and Sons Care Services Limited | Health & social care | 2021 |
| Marley's Pizza Ltd | Hospitality | 2019 |
| Marleys Fish & Chips Ltd | Hospitality | 2008 |
| Marleys Roots Limited | Other services | 2018 |
| Marlin Assets Limited | Real estate | 2017 |
| Marlina Ltd | Wholesale & retail | 2019 |
| Marline Paris Ltd | Wholesale & retail | 2025 |
| Marlow Financial Ltd | Professional & scientific | 2011 |
| Marm Solutions Limited | Wholesale & retail | 2025 |
| Marmaladebymarmalade Limited | Wholesale & retail | 2024 |
| Marmenor Ltd | Hospitality | 2015 |
| Marmoris Holdings Ltd | Financial services | 2024 |
| Marnair Services Limited | Information & communication | 2015 |
| Marnie Costumes Limited | Arts & recreation | 2016 |
| Marobee Ltd | Wholesale & retail | 2020 |
| Marocean Limited | Wholesale & retail | 2017 |
| Marodor Limited | Wholesale & retail | 2025 |
| Maronite Ltd | Wholesale & retail | 2017 |
| Maroon Vibe Ltd | Other services | 2022 |
| Marq & Muse Limited | Professional & scientific | 2025 |
| Marque Aston Ltd | Wholesale & retail | 2024 |
| Marquess Auctions Ltd | Wholesale & retail | 2024 |
| Marquess DP Ltd | Health & social care | 2016 |
| Marquette Metal Recycling Ltd | Water & waste | 2013 |
| Marquis & Sons Ltd | Construction | 2025 |
| Marr Corporation Limited | Other services | 1998 |
| Marr Homes Limited | Construction | 2020 |
| Marrey Trading Ltd | Wholesale & retail | 2021 |
| Marriott Webb Ltd | Wholesale & retail | 2023 |
| Marruecos Corner Ltd | Wholesale & retail | 2022 |
| Mars Food & Wine Ltd | Wholesale & retail | 2026 |
| Marsco Technology Limited | Wholesale & retail | 2017 |
| Marsefly Ltd | Information & communication | 2024 |
| Marsfruits Ltd | Information & communication | 2019 |
| Marsh Lane Developments Limited | Construction | 2018 |
| Marsh Tyres Ltd. | Wholesale & retail | 2011 |
| Marsh Vision Limited | Professional & scientific | 2012 |
| Marsh Williams Ltd | Information & communication | 2025 |
| Marsha Dalie Ltd | Other services | 2025 |
| Marshall Contracting (Southern) Ltd | Manufacturing | 2018 |
| Marshall Corp PC | | 2017 |
| Marshall Heating Solutions Ltd | Construction | 2020 |
| Marshall IT Limited | Information & communication | 2021 |
| Marshall SR Enterprise Ltd | Real estate | 2018 |
| Marshall Utilities Ltd | Construction | 2012 |
| Marshall Wear Ltd | Wholesale & retail | 2026 |
| Marshall Williams Ltd | Households | 2022 |
| Marshall's Auto Centre Ltd | Wholesale & retail | 2019 |
| Marsham Court (Radyr) Management Limited | Other services | 1998 |
| Marshfield Motors Ltd | Wholesale & retail | 2019 |
| Marshfield Stores Limited | Hospitality | 2002 |
| Marshlands House Limited | Hospitality | 2018 |
| Marshoak Limited | Health & social care | 2010 |
| Marsol Group Limited | Real estate | 2020 |
| Marsvrnez Ltd | Wholesale & retail | 2025 |
| Marta Laguna Ltd | Professional & scientific | 2024 |
| Martan Business PC | | 2019 |
| Martbuild Fire and Flood Ltd | Construction | 2011 |
| Martel Cleaning Ltd | Administrative & support | 2012 |
| Martel Holdings Limited | Financial services | 1990 |
| Martess Properties Limited | Real estate | 1984 |
| Martha Stone Productions Limited | Information & communication | 2017 |
| Martijn Consulting Ltd | Professional & scientific | 2024 |
| Martin & Catrin Lewis Ltd | Financial services | 2016 |
| Martin Global Sourcing Ltd | Hospitality | 2018 |