In reply to the abmmc:
One problem with digital mapping devices, especially those using OS mapping, is that the OS insist on unique digital rights management (DRM) systems being applied to their mapping. So, having paid an arm and a leg for mapping from one of the map tool suppliers (Memory Map, for instance), that mapping cannot be used with any other vendor's tools (Garmin, for instance). A crap situation, IMHO.
So, no, it's very unlikely that you will be able to load the Memory Map map tiles onto the Garmin. If you want mapping on the Garmin, you'll have to buy it all again (£200 for full OSGB 1:50k)...
What you should be able to do is transfer routes between Garmin and Memory Map.
https://www.memory-map.co.uk/support/114527-What-Garmin-GPS-units-are-compa...
I think you can at least use MM mapping with an MM app on a smartphone.