On Garmin BaseCamp the base map can sometimes show on top of the 1:25k Ordnance Survey maps you have downloaded.
How do you stop this from happening?
Double click on the downloaded mapping (the actual OS maps) and the properties dialogue box opens up.
On the right hand side you have 'Draw Order', if you move the slider to above 51 the basemap will now sit behind the Ordnance survey maps.