OK, after much tinkering and chatting to the UK Memory Map support folks here's teh full story.
1) The correct location to copy the map files is /Dowload/Memory-Map itself, not one of it's sub folders or indeed anywhere else in the tree. This should be located on the SD card (so the full path is /mnt/sdcard/Download/Memory-Map
2) The files you need to copy are NOT JUST the .qc3 file as sugested in the readme but also the .QCT file. I have in fact copied all FOUR of the os_50_gb-2012_complete files, not sure I needed them all mind you.
3) It's important NOT TO TRY to access these maps via the Digital Map Shop. If you have done, then the system will have created a "DMS" subfolder under Memory-Map and within THAT, files indicating you have not yet paid for any of the OS50 series, so it will show you the unregistered scrambled version of the map and a prompt to pay for it. Loading the full maps to the correcct location doesn't over-ride this, you will need to remove the DMS files to make MM forget you ever went there. I assume if you have paid-for DMS map files, you can work out and remove just the ones that are blocking access to the uploaded map data.
Anyway, once you have the OS50 map files loaded in the right place and have NO blocking DMS maps, if you tap into MM and tap Menu/MoreMaps, you should see the OS50s now present. When you tap them, it will check your MM online account and your device licence, and add the android device to your list of up to five registered devices. Thereafter, whenever you zoom in closer than the base-map allows, you should automatically find it moves into the greater detail of the OS50 maps.
