I've given up with Luton. Always "standby" response to initial call, I head off to remain clear and by the time they call me back (if at all) I'm always well clear and the transit not needed.
Last week thought I'd transit Gatwick enroute from Brighton to Fairoaks. Called for clearance got the "standby" so I orbited at 2,000' just south of their CTA. Then got clearance "not above 1,500" with a clearance limit of their CTZ. Another three orbits. Then got a clearance with limit BMA hangars south side. Another 2 orbits to be told "could be sometime before I can get you across due to string of inbounds". "Roger" I replied. Another orbit and cleared across the 26 threshold.
I got the feeling I wasn't really welcome and it would have been quicker to transit round the west side without troubling them (although the view not as good!).