Managed Danger Areas in the UK sector are activated by NOTAM. As mentioned, the base is not down to the surface so transit below is a possibility. Bear in mind that you might still encounter traffic below the area, although the high energy manouvreing is all likely to be within the actual MDA itself.
If they are active, you won't get a crossing service or permission to cross through them, except in an emergency situation.
Quite often the military will release the airspace back if they finish early, but won't necessarily put out a NOTAM saying so. Scottish or London FIS will be able to provide an up to date picture on the Danger Area status if you want to take a chance on the fast jets having headed home for tea and medals early.