| Manufacturing Technology Centre | |
| Manus Neurodynamica Ltd | |
| Manutech Europe Ltd | Wrexham County Borough |
| Manx Computer Bureau Ltd | Isle of Man |
| Manx Healthcare Ltd | |
| Manx Technology Group Ltd | Isle of Man |
| Manx Telecom Trading Ltd | |
| Manzeera Solutions | |
| MAP FinTech | |
| Map of Agriculture Group Ltd | |
| Maple Design Ltd | Hampshire |
| Maple Forest Marketing Ltd | |
| Mapsoft Computer Services Ltd | Devon |
| Maratopia Ltd | |
| Marc Love | Glasgow |
| Marcomz Networks | |
| Marguerite Web Design Lincolnshire | |
| Marine Biological Association | |
| Marine Cloud Ltd | |
| Marine Electronic Services Ltd | Devon |
| Marine Software Ltd | |
| Maritime Systems Ltd | |
| Mark Allan | Edinburgh |
| Mark Bridgeman | Carmarthenshire |
| Mark Design Ltd | East Sussex |
| Mark Development | |
| Mark Digital Media | |
| Mark Eslick Graphics Ltd | Hampshire |
| Mark Garwell | West Sussex |
| Mark Hatter | |
| Mark One Consultants Ltd | Somerset |
| Market Dojo Ltd | |
| Market Forever UK | |
| Market Jar | |
| Market Me | Warwickshire |
| Market Systems Ltd | |
| Marketing Automation Insider | |
| Marketing for Profits Ltd | Dorset |
| Marketing Grin | Essex |
| Marketing Kinetics | Hertfordshire |
| Marketing Lawyers | |
| Marketing Mavericks | |
| Marketing Originals | |
| Marketing Quotes | Hampshire |
| Marketing Signals Ltd | Greater Manchester |
| Marketing Solutions | Devon |
| MarketingFile | Kent |
| Marketpoint (Europe) Ltd | Berkshire |
| Marketscan Data Solutions Ltd | |
| MarketSpan | |