how about trying the canal towpaths,they can get a bit crowded in good weather (!!!) and fishermen can be a pain,but the paths are usualy pretty good and you always know which way your going,also you can cheat and ride UP the canal path on way out knowing its all DOWN hill on way back in !!! very handy if not wanting to work too hard,a lot of towpath routes also link with or are close to old ex railway tracks that have been cycle pathed,towpaths also take you through some of the greenest countryside we have left and there are 2000 + miles to explore,even in inner london there are some very nice towpath rides,though not quite as pretty as out here at watford,but metropolitian line tube takes bikes outside rush hour as do most trains.
give the towpaths a try,i'd be surprised if you did'nt enjoy !!