Thank you for the suggestion. I've just taken a look at MOBAC and got it sourcing OS Explorer... I didn't even know that was possible!

While that looks very useful if I need a specific area and know in advance, by the looks of it so far there is no way to simply load my existing QCT maps in for conversion.

I tend to end up anywhere at short notice, so really wanted to have the full UK available on a memory card. Converting what I have seems the obvious way.