The benefits of flying helicopters!
SVFR Heathrow crossing (never been refused)
London Heli-lanes (refused entry once due to ILS calibration aircraft working City; fair enough)
Transits through Gatwick, Dublin, Edinburgh, Glasgow, Aberdeen - never been refused.
All military zone transits - always have been give.
I was taught to call early. For example, Shoreham to Redhill direct, I call Gatwick as soon as I am clear of Shoreham. as I continue on route, clearance to enter the zone can come literally at the last minute but (so far) not even had to orbit. Gatwick always ask me to leave via Buckland Lake VRP but (so far) they have always been able to accepted my request in response for a hand-over to Redhill for a "sharp right" into the field.
Redhill to Shoreham I tend to go around the Western edge of Gatwick zone as the time taken to set up a crossing negates the potential benefit. The benefits of calling early!
City crossing (Lea Valley for a float-equipped helicopter offers plenty of land-clear options) there will be some orbiting 25% of the time unless the flight is Saturday PM or Sunday AM. The alternative routing to Lea Valley offered to helicopters I always refuse - I don't like the land-clear options on that one though other (better) heli pilots are happy to take it. I then elect to "remain outside" and go around the Eastern edge: so that's not a refusal by ATC, that's my decision to cancel the request.
Crossing Heathrow - I don't do that one as often. Many destinations (for me) make little difference in flight time over / around the Western edge so I don't see any advantage in adding to everyone's workload, including mine, by going over the top.