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.
The military will hand these back. It is the NATS managed AMC which decides whether the change in status is notified. Quite rationally, this decision is based upon whether anything can be gained by notifying. m there is little point raising a NOTAM saying that an activity has finished an hour early.
If they are active, you won't get a crossing service or permission to cross through them, except in an emergency situation.
Not entirely true. If the airspace is notified as active but the activity has cleared, no longer requires segregation or is handed back (as per above), you
might get a clearance through from the agencies such as London Mil.
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.
There is every possibility of high energy manouevring in the Class G airspace beneath the MDAs. The only activity you will definitely not encouter beneath the airspace is that which requires segregation.
http://www.caa.co.uk/application.asp...=detail&id=951