Considering how busy Swinley and Cannock get, having decent trail options near where people live is what will grow MTB, ,muxh as I love Wales and The Peak, they’re really not ‘day trip’ destinations for a huge chunk of the UK population.
I’m always struck by how good a shortish Red/Blue loop from Ashridge monument could be, making good use of the elevation Tom’s hill gives, starting and finishing in the (excellent) Brownlow cafe, going down the side of the hill away from the popular walkers paths.
It would need to be pretty well surfaced as Ashridge mud is a special kind of claggy horridness but with it’s proximity to the M25/A41 it would be hugely popular.
Arguably that’s a good reason not to do it, area’s busy enough already and the wealthy older locals may object, the National Trust are sadly nowhere near as pro-MTB as the FC.