Gorehounds right, I've just come across the Whitehaven to Tynemouth version of the route which the guy who's done it said was boring and easy (all roads). That doesn't sound like the St Bee's to Robin Hoods bay one to me!
So it could well be possible to do a C2C with just a spare inner tube and a mars bar in your pocket OR the full on, full fat 'just kill me now and leave my body here' route.
I know which one I'm heading for!