I've been in touch with Sustrans about the gravel, as it was they who approved it. It's upset a few people, including me! It demonstrates what the public think in general, that cyclists shouldn't have it too good. First they built the facility, then it was excellent, then they added speedbumps (no idea why, there's no speedbumps on any local roads) then the final insult is cover it with half an inch of loose gravel.
Anyway, Sustrans say that they have been supported by 'local cycling groups' as they reckon it will keep the 'speed cyclists' away, or make them slow down.
I have no idea what is going on in their heads. I guess you get the facilities that you deserve when Sustrans are involved. They do tell me that excess gravel will be swept, but I think it will still be shoot even then.