| M. A. Smith | Tapes | No tapes | No books | No hardware |
| Michael Cox Information Services | No tapes | No tapes | No books | No hardware |
| M. J. Barnes | No tapes | No tapes | No books | No hardware |
| M. Orwin | Tapes | Tapes sorted by code | No books | No hardware |
| M. R. Irving | No tapes | No tapes | No books | No hardware |
| Martin Wren-Hilton | No tapes | No tapes | No books | No hardware |
| Macmillan | No tapes | No tapes | Books | No hardware |
| Macronics | Tapes | No tapes | No books | Hardware |
| Mageco Electronic | No tapes | No tapes | No books | Hardware |
| Magnum Computing | No tapes | No tapes | No books | No hardware |
| Maplin | No tapes | No tapes | No books | Hardware |
| Martech Games | No tapes | No tapes | No books | No hardware |
| Math-Ed | No tapes | No tapes | No books | No hardware |
| Matthew Calveley | No tapes | No tapes | No books | No hardware |
| Melbourne House | No tapes | No tapes | Books | No hardware |
| Memotech | No tapes | No tapes | No books | Hardware |
| Memotronic | Tapes | No tapes | No books | No hardware |
| Michael Bredbury | No tapes | No tapes | No books | No hardware |
| Micro Computer Software | No tapes | No tapes | No books | No hardware |
| Microgame Simulations | Tapes | No tapes | No books | No hardware |
| Micromega | Tapes | No tapes | No books | No hardware |
| Mikro-Gen | Tapes | Tapes sorted by code | No books | No hardware |
| Mindseye | No tapes | No tapes | No books | No hardware |
| Mindware | Tapes | Tapes sorted by code | No books | No hardware |
| Moi | Tapes | No tapes | No books | No hardware |
| Monolith Electronics | No tapes | No tapes | No books | No hardware |
| Mosstapes | No tapes | No tapes | No books | No hardware |
| Moviedrome Video | Tapes | No tapes | No books | No hardware |
| Musamy Software | Tapes | No tapes | No books | No hardware |