| Mark Smart Weld Limited | Wholesale & retail | 2023 |
| Mark Stevens Home Improvements Ltd | Construction | 2020 |
| Mark's Ice Cream Ltd | Wholesale & retail | 2025 |
| Mark's Trains Ltd | Wholesale & retail | 2021 |
| Markerstudy Retail Group Limited | Financial services | 2025 |
| Market 7 Ltd | Wholesale & retail | 2022 |
| Market Deeping Antique and Craft Centre Limited | Real estate | 2002 |
| Market Deeping Hand Car Wash Ltd | Wholesale & retail | 2026 |
| Market FOX Ltd | Wholesale & retail | 2025 |
| Market Place (Oundle) Ltd | Health & social care | 2015 |
| Market Place Dentistry Ltd | Health & social care | 2021 |
| Market Ready (Peterborough) Ltd | Manufacturing | 2021 |
| Market Square Group Ltd | Wholesale & retail | 2008 |
| Market Street (Whittlesey) Management Company Limited | Households | 2006 |
| Marketing Consultants 786 Ltd | Professional & scientific | 2023 |
| Marketing Logistics Group Ltd | Transport & logistics | 2021 |
| Marketing People Ltd | Administrative & support | 2014 |
| Marketmagnet Solutions Ltd | Professional & scientific | 2024 |
| Marketspire Ltd | Hospitality | 2025 |
| Markia Limited | Professional & scientific | 2024 |
| Marking Films Inc Limited | Information & communication | 2017 |
| Markov and Mackie Ltd | Hospitality | 2024 |
| Marlborough Close (Devizes) Residents Company Limited | Other services | 2024 |
| Marlenaonlinecoaching Limited | Education | 2025 |
| Marley Fabrications and Welding Ltd | Manufacturing | 2018 |
| Marlor Lincoln Ltd | Extraterritorial | 2016 |
| Marlor Tooling Limited | Other services | 2002 |
| Marlow Gardner and Cooke Limited | Financial services | 1964 |
| Marnic Holdings Limited | Real estate | 2019 |
| Marnoval Ltd | Wholesale & retail | 2025 |
| Maroju Limited | Health & social care | 2023 |
| Maromi Holdings Limited | Financial services | 2023 |
| Marozas Transport Ltd | Transport & logistics | 2018 |
| Marshall Farms (Ashton) Limited | Agriculture & fishing | 2015 |
| Marshalls Plant Services Ltd | Manufacturing | 2023 |
| Marszal Trans Limited | Transport & logistics | 2018 |
| Marta Supermarket Ltd | Wholesale & retail | 2023 |
| Martello Business Services Limited | Professional & scientific | 2012 |
| Martha and Hebert Care Limited | Health & social care | 2014 |
| Martin & Hardy Logistics Ltd | Transport & logistics | 2022 |
| Martin Badley Mechanical Services Ltd | Construction | 2014 |
| Martingr Limited | Transport & logistics | 2020 |
| Martyn Edgell Antiques Limited | Wholesale & retail | 2003 |
| Marville Superstore Limited | Wholesale & retail | 2018 |
| Marvio Ltd | Transport & logistics | 2013 |
| Marvyo Ltd | Transport & logistics | 2019 |
| Marwro Ltd | Wholesale & retail | 2025 |
| Marzvin Ltd | Health & social care | 2024 |
| MAS Accountants Ltd | Professional & scientific | 2023 |
| Masaud Investments Ltd | Real estate | 2025 |
| Mask Business Consult Limited | Real estate | 2023 |
| Maskew Ltd | Information & communication | 2023 |
| Mason AV Ltd | Professional & scientific | 2024 |
| Mason's Mowers Limited | Wholesale & retail | 2010 |
| Masquet Ltd | Wholesale & retail | 2026 |
| Masrya Properties Ltd | Real estate | 2021 |
| Mass Power Supplements Limited | Wholesale & retail | 2016 |
| Massingham Electrical Ltd | Construction | 2022 |
| Mastadon Limited | Professional & scientific | 2022 |
| Master Clutch Auto Centre Ltd | Wholesale & retail | 2010 |
| Master Grid Construction Ltd | Other services | 2021 |
| Master Roofing & Home Maintenance Ltd | Construction | 2025 |
| Mastercard Prepaid Management Services Limited | Administrative & support | 2005 |
| Mastermat Build & Decor Ltd | Construction | 2025 |
| Masterminds Tuition Academy Peterborough Ltd | Education | 2019 |
| Masteroast Coffee Co. Limited | Manufacturing | 1983 |
| Masteroast Holdings Limited | Wholesale & retail | 2008 |
| Masterpac Limited | Manufacturing | 2024 |
| Mastertec Engineering Limited | Professional & scientific | 2020 |
| Mastertech Autocare Limited | Wholesale & retail | 2023 |
| Mastrella Solutions Ltd | Administrative & support | 2024 |
| Matajen Global Services Ltd | Wholesale & retail | 2023 |
| Matbus Innovations LLP | | 2025 |
| Match Point TT Events Ltd | Arts & recreation | 2024 |
| Matchless Consulting Ltd | Wholesale & retail | 2022 |
| Matchmeup Limited | Administrative & support | 2012 |
| Matcon Transport Ltd | Transport & logistics | 2026 |
| Matdor Ltd | Transport & logistics | 2021 |
| Mateo Czarny Ltd | Transport & logistics | 2023 |
| Matha Healthcare Services UK Ltd | Health & social care | 2025 |
| Mathias Financial Consultancy Ltd | Professional & scientific | 2014 |
| Matiziom Ltd | Transport & logistics | 2019 |
| Matley Dental Surgery Limited | Health & social care | 2019 |
| Matley Takeaway Ltd | Hospitality | 2018 |
| Matrix Investments (1957) Limited | Other services | 2012 |
| Matrix Studios Limited | Real estate | 2021 |
| Matrix Window Solutions Ltd | Construction | 2022 |
| Matsam Care Services Limited | Health & social care | 2015 |
| Matt Hollis Audio Services Limited | Information & communication | 2026 |
| Matt Powell Fine Jewellery Ltd. | Wholesale & retail | 2015 |
| Matte Solutions Ltd | Information & communication | 2026 |
| Matteo Transport Ltd | Transport & logistics | 2026 |
| Matter Health Limited | Health & social care | 2018 |
| Matterhorn Trading Ltd | Wholesale & retail | 2020 |
| Matthew's Van Services Ltd | Transport & logistics | 2018 |
| Matthews & Co. Heating and Plumbing Ltd | Construction | 2022 |
| Mattoni's Private Limited | Hospitality | 2023 |
| Maty Ltd | Transport & logistics | 2024 |
| Matyal Ltd | Wholesale & retail | 2024 |
| Maverick Digital Innovations Limited | Information & communication | 2022 |