London to Cumbria ~300mi - Any route planning tips?

~180mi @ 15mph - took the whole damn day and I was a wreck...

...It took me around 17 hours including breaks. The bike was a hybrid with alfine 8-speed hub gears, toestraps and panniers with not too much in them.

Nutter ;)

That's pretty hardcore.

Mini cheddars are full of energy.

Is this proven by scientists?