kytelly wrote:
I'm trying to use the journey planner to work out the best walking
routes around London.

However for anything over 1 hour it sometimes claims no route
available, but this is intermittent. I've tried ticking the various
walking only options but to no effect.

Any tips for success here?

I think you are pushing at the boundaries of its intended purpose. The
qualities of a 'best walking route' (even for reasons other than
leisure) such as taking quiet streets or passing places with aesthetic,
historical or other appeal are not ones which are embodied in the
journey planner.

Even if these qualities were somehow captured, I believe this is better
left to traditional maps, local knowledge, common sense and serendipity.
There are some aspects of our lives where we should make our own
decisions rather than entrusting them to a supposedly expert system.

ESB