| McCurrach UK Ltd | Edinburgh |
| McDonach IT Consultancy Ltd | Glasgow |
| MCG Digital Media | |
| McGinn & Dolphin​ | |
| McGregor Boyall Associates Ltd | East Sussex |
| MCI Systems Ltd | |
| McKenzies Group | Surrey |
| McLintok Internet Services Ltd | East Sussex |
| MCM | Greater London |
| McMillan Technology | Suffolk |
| MCR Systems Ltd | Leicestershire |
| MCS Global Ltd | Berkshire |
| MCS Group | Belfast |
| MCS Onsite.com | Somerset |
| MCWare IT Solutions | County Durham |
| MD Consulting | |
| MD Systems Ltd | |
| MD5 Ltd | West Yorkshire |
| MDOTM Ltd | |
| MDR Lab | |
| MDS Global | Cheshire |
| MDS Solutions | |
| Mdsign Internet Services Ltd | Suffolk |
| MDTS UK Ltd | Essex |
| ME Consultancy Ltd | West Yorkshire |
| Me Learning Ltd | |
| Me We Foundation | |
| me-too.net Ltd | West Yorkshire |
| Meadon Marketing Ltd | |
| Meadow Croft Consultants | West Yorkshire |
| Meadowlark | South Yorkshire |
| Meantime Communications | |
| Meantime IT | Cumbria |
| Measurable Ltd | |
| Measure Protocol | |
| measure2improve Ltd | Devon |
| Meatless Farm | |
| Mechtech Automation Group | |
| Med-Tech Innovation | |
| Medannex Ltd | |
| Medbelle | |
| MedCircuit | |
| MedCity | |
| MEDCO | Surrey |
| Medefer Ltd | |
| Medesk | |
| Medesk Ltd | Greater London |
| Medherant Ltd | |
| Medhurst Communications Ltd | Hampshire |
| Media Bubble Studio Ltd | |