I have specifically been trying to find out how to transfer my full GB Memory Map OS 1:50K 2012 GB map to an iPad, finally found a working solution here.
Basically find your *.qct and *.qc3 file and transfer them to memory map through the iTunes app section. Memory Map must not be running on the device while doing this.
To view the maps start Memory Map then go to Folder, More Maps, All Maps on Device.
It is worth checking Map Types as new detected types seem to default with a disabled view, the 2012 GB is type ‘Land’. Turn this on and then then ‘OS 1:50k Great Britain’ should show up. on first view it will ask to use one of your 5 enables.