Generally find transits not too bad - most recent examples are Solent, Brize Norton, East Midlands - although EM was inbound to Tollerton so it is pretty much on route when from the South!
HAd an interesting one recently where overhead Newbury en route to Wellesbourne I called Brize for a transit of the eastern side of the zone and was told to call Farnborough?
Actually routed around and carried on listening to Brize - did not seem that busy but who knows. Coming back later the same day the Wx was slightly better so routed over the top of the zone at 4000ft.
I agree it often seems to help if you can call early and sound like you know what you are talking about and keep it concise. I have heard lots of life histories which make it difficult for all of us - especially if you have been asked to report at a certain point .....
Have to query the comment from the glider pilot earlier - you want to talk to ATC but gliders generally will not carry a transponder because it's too heavy - surely if you want a better service from them you could at least help them?
Edited to add - just read the post above and have to say it sounds great. Have not been towards Bristol recently but wish (from a pilots perspective) it was sometimes more like that elsewhere.
TZ