I think the whole concept is absolutely mental. Pretty much the same as survival tins, but on a bigger scale. Where exactly do people plan to go once they've 'bugged out' in the UK?
Ideally to whatever shelters the authorities see fit to open; over here the counties and cities usually open the public schools (particularly the school gymnasiums) as official shelters, with the Red Cross assisting. Otherwise to stay with relatives who live away from the affected evacuation area. Or even as Red posted, in a hotel outside the affected area.
I agree the TEOTWAWKI or Zombie Appocalypse scenarios are fantasy, but natural disasters and major accidents do indeed happen. Over here (at least in Florida) it's mostly hurricanes; there I remember mostly snow emergencies as far as natural events go. As Red mentioned, floods are also possible (even probable from time to time) there and here. Out West wildfires are a real threat; I don't remember that ever occurring in the UK but I wouldn't want to rule it out, especially if you ever get periods of drought.
Apparently from some of the links posted, the UK authorities, and local counsels also have some concerns.