The campaign for better transport did a headline grabbing study a while back that for cycling & walking ranked various cities in this order:-
1 NOTTINGHAM
2 MANCHESTER
2 CAMBRIDGE
4 MILTON KEYNES
5 BRIGHTON AND HOVE
6 NEWCASTLE
6 BRISTOL
8 SOUTHAMPTON
8 PLYMOUTH
10 LONDON
10 LIVERPOOL
12 LEEDS
13 LEICESTER
13 LUTON
15 PETERBOROUGH
16 SUNDERLAND
17 BIRMINGHAM
18 COVENTRY
19 SHEFFIELD
I'm Pleased to see Newcastle up at number 6. I've just been there for work and had to cycle fom the city's main station to a business park just west of Scotswood (only about 4 or 5 miles) and it was a brilliant ride. It was right alongside the river Tyne pretty much all the way (Route 72), mostly away from the road- v. enjoyable. Big thumbs up from me for the place all round really- seemed like a great city, only wish I'd had more time to explore further. Only downside was right at the end, trying to cycle up a road called Forth Banks, when rushing for a train on a Brompton, is not a great idea - especially for a Fenlander- that street must be about 1:3 !
I'd also nominate Birmingham- just for the network of canals enabling fast, pleasant riding into the place from all around. Peterborough is also pretty good- some nice routes along the river.
Bottom of my list would easily be London, although I am biased as I abslolutely loathe the place- you seem to need an extra sense there just to make sense of it all- mental. But rather cycle there than attempt to use their utterly shambolic public transport system.