| Mapleoak Resourcing Limited | Administrative & support | 2016 |
| MAR Fish Bar Ltd | Hospitality | 2016 |
| Marabusu Ltd | Wholesale & retail | 2026 |
| Marbasa Ltd | Wholesale & retail | 2021 |
| Marble and Saffron Limited | Real estate | 2025 |
| Marble Scale Ltd | Information & communication | 2026 |
| Marbledairy Consulting Limited | Administrative & support | 2012 |
| Marbles & Diamonds Ltd | Wholesale & retail | 2022 |
| Marcella Medical Ltd | Health & social care | 2025 |
| March Hare Floral Design Limited | Agriculture & fishing | 2016 |
| Marcharh Ltd | Professional & scientific | 2017 |
| Marchen (Property Development) Limited | Real estate | 1973 |
| Marchi Technologies Limited | Information & communication | 2026 |
| Marco Matteo Asset Management Ltd | Real estate | 2026 |
| Marco Pony Ltd | Wholesale & retail | 2025 |
| Marcus Harley Limited | Construction | 2016 |
| Marcus Reddy Enterprises Ltd | Wholesale & retail | 2016 |
| Marcus Reddy Limited | Health & social care | 2008 |
| Marcus Stokes Limited | Extraterritorial | 2016 |
| Marcus's Motor Rentals Limited | Administrative & support | 2006 |
| Mardon Distribution Limited | Other services | 2017 |
| Maret Ltd | Wholesale & retail | 2026 |
| Marfield Property Maintenance Ltd | Construction | 2017 |
| Marfleet and Bradshaw (East Anglia) Limited | Construction | 2023 |
| Marfran Productions Limited | Information & communication | 2018 |
| Maria Bageta Ltd | Health & social care | 2025 |
| Maria Eugenia Consulting Ltd | Health & social care | 2023 |
| Marian Retail Ltd | Wholesale & retail | 2025 |
| Maribo Holdings Limited | Financial services | 2026 |
| Marigold Real Estate Ltd | Real estate | 2022 |
| Marine Master Ltd | Manufacturing | 2018 |
| Marine Surveys International Ltd | Professional & scientific | 2022 |
| Mark Alan Peter Richards Limited | Other services | 2025 |
| Mark Bainbridge Consultancy Ltd | Professional & scientific | 2023 |
| Mark Harvey Renewables Ltd | Construction | 2025 |
| Mark Hill Investments Ltd | Financial services | 2026 |
| Mark Howlett Limited | Wholesale & retail | 2012 |
| Mark Jennings Lane RTM Company Limited | Real estate | 2011 |
| Mark Leonard Davies Ltd | Extraterritorial | 2024 |
| Mark This for ME Ltd | Information & communication | 2023 |
| Mark Thompson Legal Limited | Professional & scientific | 2014 |
| Markel Secure Ltd | Administrative & support | 2026 |
| Market Cross Smile Studio Ltd | Education | 2025 |
| Market House Hotel Limited | Hospitality | 1982 |
| Market Thoroughfare (BSE) RTM Company Limited | Households | 2024 |
| Marketplace Maestro Ltd | Wholesale & retail | 2023 |
| Markham Brunswick Estates Limited | Real estate | 1996 |
| Markits Professional Builders Limited | Construction | 2024 |
| Markov Hospitality Limited | Administrative & support | 2024 |
| Marks & Cristin Limited | Extraterritorial | 1999 |
| Markup Design Ltd | Professional & scientific | 2019 |
| Marky's Pubs Limited | Hospitality | 2019 |
| Marlailerdo Ltd | Financial services | 2025 |
| Marley Laser Holdings Limited | Professional & scientific | 2020 |
| Marlissa Capital (Midlands) Ltd | Real estate | 2025 |
| Marlissa Capital Ltd | Real estate | 2023 |
| Marmo Capital LLP | | 2023 |
| Marmoset Games Ltd | Information & communication | 2024 |
| Marni Investments Ltd | Real estate | 2019 |
| Marp Corp Ltd | Information & communication | 2020 |
| Marriage Sponsor Protection UK CIC | Education | 2025 |
| Marry the World Ltd | Information & communication | 2026 |
| Marsh Developments (GBR) Ltd | Financial services | 2023 |
| Marsh Property Management Ltd | Construction | 2008 |
| Marshall Creations Ltd | Manufacturing | 2025 |
| Marshall Method Publishing Ltd | Information & communication | 2012 |
| Marshall Method Therapy Ltd | Health & social care | 2014 |
| Marshall's Consultancy Limited | Professional & scientific | 2024 |
| MART24 Ltd | Wholesale & retail | 2020 |
| Martha V Limited | Wholesale & retail | 2008 |
| Martin and Darren Properties Limited | Real estate | 2020 |
| Martin Construction Southern Ltd | Construction | 2014 |
| Martin Hannah Limited | Information & communication | 2026 |
| Martin Higginson Ltd | Education | 2014 |
| Martin Middleton Therapy Ltd | Health & social care | 2025 |
| Martin's Motors (Suffolk) Limited | Wholesale & retail | 2022 |
| Martins Furnishers Limited | Wholesale & retail | 2013 |
| Marvellous YOU Limited | Wholesale & retail | 2025 |
| Marvelous Enteprises Ltd | Information & communication | 2020 |
| Marvin Works Ltd | Information & communication | 2026 |
| Marximum Volume Ltd | Arts & recreation | 2025 |
| Mash Research Consultancy Limited | Professional & scientific | 2025 |
| Maslom Limited | Information & communication | 2016 |
| Mason B Property Ltd | Real estate | 2025 |
| Mason Doyle Solutions Limited | Administrative & support | 2025 |
| Masona Limited | Administrative & support | 2026 |
| Masonlane Limited | Extraterritorial | 2025 |
| Mass Creations Ltd | Information & communication | 2020 |
| Mass Heavy Industrie Ltd | Arts & recreation | 2023 |
| Mastermind Arbitrage Ltd | Information & communication | 2025 |
| Masters Development Management Ltd | Professional & scientific | 2019 |
| Mastersales App Ltd | Information & communication | 2026 |
| Masuzi Limited | Manufacturing | 2018 |
| Mataniciva Services Ltd | Administrative & support | 2021 |
| Match WIN Sports Ltd | Wholesale & retail | 2024 |
| Matchcut Agency Ltd | Wholesale & retail | 2025 |
| Matched CIC | Information & communication | 2024 |
| Matchwork Ltd | Information & communication | 2026 |
| Mateo's Adventures With Nana Ltd | Real estate | 2024 |
| Material Funding Ltd | Construction | 2020 |