Hi Leadhead.
LFAJ, and ShyTorque have it about covered.
...is it really possible to do a long flight out of radio contact in Britain?
I suppose it depends what you call a long flight.
You can fly the entire length of UK airspace direct from Dover, by the English Channel, to the Shetland Islands, in the north of Scotland,(600nm+) at 3,000' without talking to anyone.
In my opinion, the sooner we get rid of the archaic RPS and introduce a common UK/Europe wide TA the better.
MJ