| Mulberry Square Ltd | |
| Mullan Training | Belfast |
| Multi Circuit Boards Ltd | Dorset |
| Multi Media Replication | Hampshire |
| Multi-Health Systems, Inc. | Belfast |
| Multimedia Monkey | Cardiff |
| Multimedia Projects Ltd | Kent |
| Multiomic Health Ltd | |
| Multiple Access Communications Ltd | Hampshire |
| Multipulse Electronics Ltd | Surrey |
| Multitek Ltd | Essex |
| Multithread Consultants Ltd | Suffolk |
| MultiTime Systems Ltd | Greater London |
| Multitone Electronics plc | Hampshire |
| Multiverse | |
| Multivitamin Studio | |
| Multus Biotechnology | |
| Mulvaney Capital Management Ltd | |
| Munch Studio Ltd | |
| Munky Online | Suffolk |
| Munro Agency | |
| Muon Software | Lincolnshire |
| Mursla Ltd | |
| Mushroom Components | Bedfordshire |
| Musicverse Ltd | |
| Mustard Design Ltd | Hampshire |
| Mustard Seed | Greater London |
| Mutual Advantage Ltd | Suffolk |
| MVF Global | |
| MVM Partners, LLP | |
| MW Consultancy Ltd | West Yorkshire |
| MWA Software | Hampshire |
| MXB Agency | |
| MXC Capital Ltd | Channel Islands |
| My AskAI | |
| My CRM Ltd | Isle of Wight |
| My Customer Lens | |
| My Domain Name | Hampshire |
| My Social Agency Ltd | West Yorkshire |
| My Type Of People Marketing | |
| My Voice AI Ltd | |
| My1login Ltd | Glasgow |
| My360Plus | |
| MyAllSearch | |
| MyAssays Ltd | East Sussex |
| myCloud Media Ltd | |
| Myco Holdings plc | North Yorkshire |
| Myco Systems Ltd | |
| mycom-osi | Berkshire |
| MyEdSpace Ltd | |