In reply to Andy Cairns:
> He says fell or cross country running shoes definitely don't have enough shock-absorbing if there is any hard surface to be covered, and will cause blisters more quickly.
NB By the OP's 'ordinary running trainers', I understood road-running shoes. Which I wear for everything I can (including many rough off-road courses) for pretty well the reasons you cite.
> He says unless it's bone-dry you WILL get wet feet, either through sweat or water getting in and a blister kit is essential after about 50 miles.
Trainers let water in and water out, which works! Unless they're Goretex-lined types (like some approach shoes), which let it in (over the tops) but not out again. And, while I'd agree with c.50 miles re. blistering soles, I've found my heels/toes etc. generally survive in road shoes where they more often suffer in hill/trail shoes. (Caveat: we're all different!)