| Marlan Maritime Technologies Ltd | |
| Marlin Web Design | Greater Manchester |
| Marmalade Game Studio | |
| Marnix Garner | Hertfordshire |
| Marquee Tech Ltd | |
| Marriott Design | |
| Martel Instruments | |
| Martin Dawes Ltd | Cheshire |
| Martin Woods | |
| Martin Wright | |
| Martlet Capital Ltd | |
| Marval Software | Northamptonshire |
| Marvel | |
| Marvellous | West Yorkshire |
| Marward Services Ltd | Buckinghamshire |
| Marzee | |
| Marzee Labs | Greater London |
| Masabi Ltd | |
| Mash Media UK Ltd | |
| Mashauri | |
| Mason Infotech | Nottinghamshire |
| Mass plc | Berkshire |
| Massive Analytic Ltd | |
| Massive Ltd | Leicestershire |
| Master SEO UK | |
| Mastered | |
| Masters of Pie Ltd | |
| Masters.Cloud | |
| MasterSeries | Mid and East Antrim |
| Mastodon C | |
| Mat & Mouse IT Services Ltd | South Yorkshire |
| Matchingham Games | |
| MatchMaker Software Ltd | West Midlands |
| Matchtech Group (UK) Ltd | Hampshire |
| Matek Business Media | |
| Math Quiz | |
| MathFiles | Herefordshire |
| Mathieson Financial Services | |
| Maths is Good for You | Somerset |
| Maths Star | Kent |
| MathsChallenge.net | Surrey |
| Mathsframe Ltd | Warwickshire |
| MathSphere | West Sussex |
| Matillion Ltd | Greater Manchester |
| Matley Software Ltd | Greater Manchester |
| MatNex | |
| Matrix e-Business | Newport |
| Matrix iQ | |
| Matrix Marketing and Media Solutions Ltd | Devon |
| Matrix Platinum Ltd | Lancashire |