| Mark Hewitson Stone & Ceramic Tiling Ltd | Construction | 2013 |
| Mark Hughes Limited | Arts & recreation | 2002 |
| Mark Noble Limited | Professional & scientific | 2024 |
| Mark Slater Photography Limited | Professional & scientific | 2021 |
| Mark Swatts Morse LLP | | 2011 |
| Mark Thorpe Fabrication Limited | Manufacturing | 2026 |
| Mark Toney & Company Limited | Hospitality | 1952 |
| Mark Tose Kitchen Solutions Ltd | Administrative & support | 2022 |
| Mark Tose Kitchens & Bedrooms Ltd | Construction | 2019 |
| Mark Tricoglus Limited | Real estate | 2014 |
| Mark Turner Maintenance Limited | Construction | 2019 |
| Mark Wait Funeral Services Ltd | Other services | 2022 |
| Mark Wright Tech Ltd | Professional & scientific | 2024 |
| Marka Rating Limited | Professional & scientific | 2024 |
| Markbourn 1 Limited | Real estate | 2017 |
| Markbourn II Limited | Real estate | 2025 |
| Markbourn Limited | Real estate | 1997 |
| Marked Safe Ltd. | Professional & scientific | 2024 |
| Market Shaker Ltd | Administrative & support | 2019 |
| Marketing Position Limited | Professional & scientific | 2017 |
| Markit Placements Ltd | Administrative & support | 2017 |
| Marksummershair Ltd | Other services | 2025 |
| Marktday Ltd | Information & communication | 2025 |
| Marla Club Limited | Arts & recreation | 2026 |
| Marlborough House (Newcastle) Holdings Limited | Real estate | 2018 |
| Marlborough Social Club (Newcastle) Limited | Hospitality | 2017 |
| Marleen Investment Group Ltd | Real estate | 2025 |
| Marley Hill Estates Ltd | Agriculture & fishing | 2016 |
| Marlin UK Limited | Wholesale & retail | 2017 |
| Marmaris Barberz Ltd | Other services | 2025 |
| Marmont Encore Limited | Arts & recreation | 2023 |
| Marney Electrical Limited | Energy | 2025 |
| Marra Cars Ltd | Transport & logistics | 2025 |
| Marra Limited | Administrative & support | 2020 |
| Marrabio Limited | Professional & scientific | 2022 |
| Marrime Limited | Wholesale & retail | 2006 |
| Mars Barbers Ltd | Other services | 2024 |
| Mars Food Fusion Ltd | Hospitality | 2026 |
| Mars Medical Limited | Health & social care | 2018 |
| Marsden Specialist Surveys Ltd | Households | 2025 |
| Marseilles Chambers RTM Company Limited | Households | 2012 |
| Marsfen Architecture Ltd | Professional & scientific | 2013 |
| Marshall Branson Marine Limited | Energy | 1990 |
| Marshall Housing Company Ltd | Real estate | 2021 |
| Marshall Inns Limited | Extraterritorial | 2001 |
| Marshall Merritt Electrical Limited | Construction | 2021 |
| Marshall-Huang Limited | Wholesale & retail | 2008 |
| Marshalls Tree Surgeons Ltd | Agriculture & fishing | 2011 |
| Marshbrand Limited | Other services | 2018 |
| Marshmallow Global Ltd | Information & communication | 2024 |
| Marspa Ltd | Health & social care | 2021 |
| Marstone Properties Limited | Real estate | 2026 |
| Martin Bell Design Solutions Ltd | Professional & scientific | 2011 |
| Martin Rankin Funeral Directors Ltd | Health & social care | 2010 |
| Martin Rimmer Consulting Ltd | Professional & scientific | 2019 |
| Martin Tait Redheads Ltd. | Professional & scientific | 1977 |
| Martina Collins Dental and Skin Clinic Ltd | Health & social care | 2014 |
| Martis George Enterprises Ltd | Wholesale & retail | 2025 |
| Martology Limited | Wholesale & retail | 2024 |
| Marvin Property Ltd | Real estate | 2021 |
| Mary Cronin Management Limited | Wholesale & retail | 2012 |
| Mary Nail & Beauty Ltd | Other services | 2023 |
| Mary Perry Ltd | Construction | 2016 |
| Mary's Jade Garden Limited | Hospitality | 2021 |
| MAS Machinery Limited | Wholesale & retail | 2025 |
| MAS Optic Limited | Wholesale & retail | 2019 |
| Masaeef Ltd | Wholesale & retail | 2025 |
| Masamss Limited | Wholesale & retail | 2026 |
| Masamune Tattoos Ltd | Arts & recreation | 2018 |
| Mascot Services Limited | Manufacturing | 1988 |
| Mash Medicolegal Ltd | Health & social care | 2024 |
| Mash Property Ltd | Real estate | 2017 |
| Mashaf Trading Limited | Wholesale & retail | 2024 |
| Maskani Ltd | Construction | 2020 |
| Maslar Limited | Professional & scientific | 2006 |
| Mason and MAE Limited | Information & communication | 2026 |
| Mason Construction (NE) Ltd | Construction | 2022 |
| Mason Fixings Limited | Construction | 2018 |
| Mason Frank International Limited | Administrative & support | 2010 |
| Mason Properties NE Ltd | Construction | 2024 |
| Masouds Barber Limited | Other services | 2018 |
| Massa 46 Ltd | Administrative & support | 2018 |
| Massive Coast Ltd | Information & communication | 2018 |
| Massive Objects Ltd | Manufacturing | 2022 |
| Masteck Limited | Information & communication | 2003 |
| Master Stitch & Dog and Home Ltd | Manufacturing | 2024 |
| Masterman Young Ltd | Professional & scientific | 2022 |
| Masterprior Limited | Other services | 1991 |
| MAT22 Ltd | Hospitality | 2024 |
| Mata Enterprises Limited | Transport & logistics | 2010 |
| Matcha ERA Ltd | Hospitality | 2021 |
| Matcha Events Ltd | Administrative & support | 2023 |
| Matchbox Pizza Company Ltd | Hospitality | 2025 |
| Matchpoint Sport Ltd | Arts & recreation | 2025 |
| Matdom Web Design Limited | Professional & scientific | 2004 |
| Mate's Barbers NE Ltd | Other services | 2025 |
| Materials Solutions Limited | Manufacturing | 2014 |
| Matex (UK) Limited | Hospitality | 2003 |
| Matfen Black Bull Limited | Hospitality | 2003 |
| Matfen Energy Limited | Administrative & support | 2010 |