I was curious about some of the concern above about narrow lanes and cycling trails. There are so many side roads in Britain that one rarely has to ride on a road in fast traffic or a cycle way (see rivers RWGPS route above). It takes longer, but who rides a bike to get anywhere fast?
For my rides in Britain - or I suppose anywhere else (I ride about 100 miles a week) it is fun to actually 'ride' the entire route beforehand by using Google Street View.
From my observation (I grew up in Norwich) Britain offers the very best in scenery and quaintness for the cyclist.