I relative of mine used to work at NATS Swanwick as well and I have had several visits there, one in fact before the facility was actually open - was certainly a weird experience wondering around all these radar screens which were on and running but had no one manning them.
All the controllers I met seemed very professional - sitting down and listening to the Heathrow Director frequency for example while next to the actual controller was very impressive.
In the air I've never had the feeling in the UK the ATC wasn't sympathetic to my general aim to reach my destination in a timely fashion even if crossing the London Terminal Control Area in a C182 at 140kts isn't exactly making life easy for them. That said I have overheard some exchanges similar to what RAPA Pilot mentions...a bit of patience from both sides and things are easier.