I know of a couple of local farms, who still have PYO, and farmshops with seasonal produce, which has been ready picked. However, I can't really see millions of city dwellers going into the countryside to pick their fruit and veg rather than nipping to the local supermarket. The carbon footprint of all those cars leaving cities is, in any case, probably higher than taking produce to market in lorries.
Ironically, we could end up with more imported fruit and veg, because labour abroad is cheaper, which might offset higher transport costs. It would probably be worthwhile growing, picking and freezing/canning some fruit and veg then importing to the UK.