| Ministry of Paint Ltd | Administrative & support | 2019 |
| Mintbint Ltd | Professional & scientific | 2023 |
| Mintronics Limited | Information & communication | 2008 |
| Mischiefs Leisure Limited | Administrative & support | 2015 |
| Missing Textures Ltd | Professional & scientific | 2022 |
| Mist Property Solutions Ltd | Real estate | 2016 |
| Mitchell Gordon LLP | | 2010 |
| Mj's Cake Cafe Ltd | Wholesale & retail | 2022 |
| Mjackson Engineering Ltd | Professional & scientific | 2024 |
| MJE Interiors Ltd | Professional & scientific | 2022 |
| MJM Music Ltd. | Arts & recreation | 2018 |
| MJP Digital Ltd | Information & communication | 2016 |
| MJS Construction & Maintenance Ltd | Construction | 2022 |
| MJS UKV Limited | Wholesale & retail | 2021 |
| MJW Catering Ltd | Hospitality | 2025 |
| MK Inspection Services Limited | Professional & scientific | 2017 |
| MK Ladach Ltd | Transport & logistics | 2025 |
| Mkanya Social Care Ltd | Health & social care | 2021 |
| Mkfl Ltd | Wholesale & retail | 2018 |
| MKH Goods Ltd | Wholesale & retail | 2023 |
| Mkra Limited | Professional & scientific | 2025 |
| ML Driveways-Patios & Groundworks Ltd | Construction | 2023 |
| Mljb Holdings Limited | Financial services | 2026 |
| MLN (Locum) Ltd | Health & social care | 2026 |
| MLR Logistic Transport Limited | Transport & logistics | 2020 |
| MMB Properties Ltd | Construction | 2001 |
| Mmcd&A Ltd | Health & social care | 2023 |
| MMK Motor Company Ltd | Wholesale & retail | 2015 |
| Mmkj Holdings Partnership LLP | | 2024 |
| Mmkj Ltd. | Wholesale & retail | 2016 |
| Mmmotorcompany Ltd | Wholesale & retail | 2025 |
| MMT Motorcycles Ltd | Wholesale & retail | 2026 |
| MN Consultancy Limited | Financial services | 2004 |
| MNS Transport Limited | Transport & logistics | 2020 |
| Moansey Limited | Real estate | 1975 |
| Moanspace Limited | Information & communication | 2010 |
| Mobile City Magic Vape Ltd | Wholesale & retail | 2023 |
| Mobile DPF Cleaning Ltd | Wholesale & retail | 2016 |
| Mobile Repair Solutions Ltd | Information & communication | 2023 |
| Mobilez World Ltd | Other services | 2011 |
| Mobius Consultancy Ltd | Education | 2017 |
| Moco Claims and Services Limited | Professional & scientific | 1995 |
| Moco Group Limited | Professional & scientific | 2015 |
| Modena Solutions Ltd | Administrative & support | 2023 |
| Moderncity Construction Ltd | Construction | 2016 |
| Modular Cladding Systems Limited | | 1986 |
| Modular Manpower Ltd | Manufacturing | 2025 |
| Modus Technical Consulting Limited | Construction | 2024 |
| Modus Technologies Ltd | Professional & scientific | 2025 |
| Mojo Entertainment Limited | Other services | 2017 |
| Mojo Mushrooms Ltd | Agriculture & fishing | 2026 |
| Mojoa Limited | Other services | 2010 |
| Molrs Wholesale Limited | Wholesale & retail | 2026 |
| Momento Bishop Ltd | Hospitality | 2026 |
| Momento Durham Ltd | Hospitality | 2026 |
| Monayglobal Services Limited | Transport & logistics | 2023 |
| Monk. Craft Beer Ltd | Manufacturing | 2026 |
| Monkend Properties Ltd | Real estate | 2020 |
| Monolith Conservation Ltd | Construction | 2016 |
| Monolith Estates Ltd | Construction | 2021 |
| Monomer Plastics Recycling Ltd | Manufacturing | 2025 |
| Montan Lago Limited | Hospitality | 2002 |
| Mooda Drinks Ltd | Manufacturing | 2025 |
| Moonrise Facilities Limited | Professional & scientific | 2022 |
| Moonstone Ventures Ltd | Administrative & support | 2025 |
| Moore Lettings Limited | Real estate | 2025 |
| Moorside Groundworks Ltd | Administrative & support | 2021 |
| Moortrim Auto Upholstery Ltd | Manufacturing | 2021 |
| Mordon Lodges Limited | Hospitality | 2023 |
| Morgan Moran Ltd | Professional & scientific | 2021 |
| Morgan Robson Finance Ltd | Financial services | 2023 |
| Morits Events Management Limited | Hospitality | 2019 |
| Morland-Bainbridge-Nixon Limited | Real estate | 2022 |
| Morrison Cook Collective Limited | Administrative & support | 2024 |
| Morton Park Automobility Ltd | Wholesale & retail | 2022 |
| Mossman & Co Developments Ltd | Construction | 2008 |
| Motive Performance Modified & Classic Cars Limited | Wholesale & retail | 2025 |
| Motorclips Ltd | Wholesale & retail | 2014 |
| Motors on TAP Limited | Wholesale & retail | 2025 |
| Movepatw Ltd | Wholesale & retail | 2025 |
| Movinn Plus Ltd | Transport & logistics | 2025 |
| Mowden Coffee House Ltd | Hospitality | 2026 |
| MPH Electrical Contractors Limited | Construction | 2019 |
| MPM GAS Services Ltd | Construction | 2014 |
| MPR Medic & Safety Ltd | Health & social care | 2019 |
| MPS Companies Limited | Wholesale & retail | 2018 |
| MR Boost Ltd | Wholesale & retail | 2023 |
| MR Martin Mccaskill Ltd | Information & communication | 2015 |
| MR Midnight Ltd | Arts & recreation | 2021 |
| MR Projects Limited | Professional & scientific | 2012 |
| MR Shawarma Darlington Ltd | Hospitality | 2026 |
| MR Singh Homes Ltd | Real estate | 2024 |
| MR Vape Darlington Limited | Wholesale & retail | 2025 |
| MR. Cheaper Ltd | Wholesale & retail | 2025 |
| MRC Logistic Services Ltd | Transport & logistics | 2026 |
| MRC Roads Limited | Construction | 1996 |
| MRG Automotive Ltd | Professional & scientific | 2023 |
| MRS Palmer’S Pantry Limited | Hospitality | 2019 |
| MS Support Ltd | Transport & logistics | 2021 |
| Msavehu Ltd | Wholesale & retail | 2025 |