| M & NW Property Limited | Real estate | 2022 |
| M & NW Property Maintenance Limited | Real estate | 2023 |
| M & S Windings Limited | Real estate | 1990 |
| M a Watt Construction Limited | Construction | 2017 |
| M and D Groundworks Ltd | Construction | 2013 |
| M C Building & Renovation Ltd | Construction | 2022 |
| M C Nichols Limited | Construction | 2003 |
| M C Services (Devon) Ltd | Wholesale & retail | 2007 |
| M Channing Ltd | Construction | 2025 |
| M Davey Carpentry Ltd | Construction | 2018 |
| M G R Car Valeting Ltd | Administrative & support | 2025 |
| M Harris Holdings Limited | Financial services | 2024 |
| M J Alexander Properties Limited | Real estate | 2018 |
| M J C (Devon) Contractors Limited | Construction | 2010 |
| M J Stevens Ltd | Construction | 2008 |
| M K Trade Sales Ltd | Wholesale & retail | 2021 |
| M P Goldsmith Limited | Construction | 2009 |
| M P K (Holdings) Limited | Financial services | 2014 |
| M P K Developments Limited | Construction | 2015 |
| M R Deliveries Ltd | Transport & logistics | 2024 |
| M R Family Properties Limited | Real estate | 2023 |
| M Rose Engineering Limited | Wholesale & retail | 2014 |
| M W Decorators & Building Services Ltd | Construction | 2013 |
| M&C Dent Ltd | Health & social care | 2025 |
| M&C Health Solutions Ltd | Health & social care | 2023 |
| M&G Property Consultants Limited | Real estate | 2025 |
| M&G Property Services Ltd | Real estate | 2018 |
| M&L Carpentry and Building Ltd | Manufacturing | 2025 |
| M&L Properties (SW) Ltd | Real estate | 2021 |
| M&L Transport (NW) Ltd | Transport & logistics | 2023 |
| M&M Delivery Services Ltd | Transport & logistics | 2026 |
| M&M Tyres Ltd | Financial services | 2024 |
| M&R Building Construction Ltd | Construction | 2024 |
| M&S Revive Ltd | Real estate | 2018 |
| M.A. Hairstyles (Devon) Limited | Other services | 2012 |
| M.A.R Electrical Contracting Ltd | Other services | 2016 |
| M.A.T. Electrics Limited | Construction | 1998 |
| M.E.D. Planning Limited | Professional & scientific | 2017 |
| M.Evans Electrical Services Ltd | Construction | 2023 |
| M.H.S.Support Ltd | Health & social care | 2021 |
| M.I.S Catering Limited | Hospitality | 2013 |
| M.J. Smith & Co Limited | Professional & scientific | 2002 |
| M.O.C Prestige Homes Ltd | Administrative & support | 2014 |
| M.R.B.T. Limited | Transport & logistics | 2017 |
| M.S. Build Right Ltd | Construction | 2026 |
| M.V. Clatworthy Limited | Construction | 1976 |
| M4 Auto Tech Solutions Limited | Wholesale & retail | 2024 |
| M4L C&R Services Ltd | Administrative & support | 2026 |
| M5 Marine Limited | Manufacturing | 2014 |
| MA Commercial Services Limited | Professional & scientific | 2011 |
| MA Property Company Limited | Real estate | 2022 |
| Mabel & Co (UK) Ltd | Other services | 2014 |
| Macanosw Ltd | Transport & logistics | 2018 |
| Machina Augmensis Ltd | Financial services | 2023 |
| Machine Doctor - CBM Services Ltd | Professional & scientific | 2024 |
| Machine Serve Ltd | Extraterritorial | 2010 |
| Mackney Purbeck Stays Limited | Hospitality | 2026 |
| Maclean Solutions Limited | Information & communication | 2003 |
| Macquisten Consultants Ltd | Professional & scientific | 2015 |
| Macra Engineering Ltd | Manufacturing | 2017 |
| Macro Shack (SW) Ltd | Hospitality | 2024 |
| Macrocarpa Limited | Professional & scientific | 2022 |
| Macrotech (Contracts) Limited | Construction | 1989 |
| Mada Logistics Ltd | Transport & logistics | 2018 |
| Made by Prism Ltd | Information & communication | 2013 |
| Made for YOU Gifts Ltd | Wholesale & retail | 2020 |
| Made in England Group Ltd | Wholesale & retail | 2026 |
| Madison Wyatt Limited | Other services | 2015 |
| Madrigal Investments Ltd | Real estate | 2013 |
| MAE Homes SW Ltd | Real estate | 2023 |
| Maehair Ltd | Other services | 2021 |
| Maenne Limited | Construction | 2019 |
| Maer Beach Limited | Hospitality | 2017 |
| Maesgwynne Properties Limited | Real estate | 1965 |
| Mafcase UK Ltd | Manufacturing | 2025 |
| MAG Windows Ltd | Construction | 2018 |
| Magd Ltd | Health & social care | 2019 |
| Magdalen Cheese & Provisions Limited | Wholesale & retail | 2021 |
| Magdalen Health Limited | Health & social care | 2015 |
| Magdalen Place Management Company Limited | Real estate | 2013 |
| Magdalen Wellbeing Ltd | Arts & recreation | 2020 |
| Magic Touch Painters and Maintenance Ltd | Construction | 2026 |
| Magneum Limited | Households | 2024 |
| Magnolia Coffee Shop Ltd | Hospitality | 2006 |
| Magnum Opus Aesthetics Ltd | Wholesale & retail | 2024 |
| Magpies Topsham Ltd | Wholesale & retail | 2026 |
| Mahoosive Fitness Ltd | Arts & recreation | 2025 |
| Maia Ventures Limited | Transport & logistics | 2010 |
| Maiden Head Energy Limited | Energy | 2024 |
| Main Street Group Ltd | Professional & scientific | 2021 |
| Maisie Match Ltd | Wholesale & retail | 2025 |
| Maison DU Soleil Ltd | Other services | 2025 |
| Maison LE Grand Properties Limited | Real estate | 2016 |
| Major Trees Ltd | Agriculture & fishing | 2005 |
| MAK Holding Limited | Professional & scientific | 2015 |
| MAK Investment Properties Ltd | Real estate | 2019 |
| MAK Sourcing Limited | Real estate | 2019 |
| Maker Coating Systems Limited | Wholesale & retail | 1979 |
| Maketank Ltd | Arts & recreation | 2018 |
| Makeup Happy Ltd | Other services | 2023 |