Update. I went exploring a few back up options for this the other day, and (barring prolonged crap weather turning everywhere into a gloop-fest), I'm now happy there are enough alternative routes to ensure anyone on a more gravel/monstercross type bike can get round. 40c or bigger, with a decent amount of tread will see you right.
Update. I went exploring a few back up options for this the other day, and (barring prolonged crap weather turning everywhere into a gloop-fest), I'm now happy there are enough alternative routes to ensure anyone on a more gravel/monstercross type bike can get round. 40c or bigger, with a decent amount of tread will see you right.