Debt free or away from densly populated areas when SHTF?

[bigpaul]

you don't say where you are in London, so a move to Surrey might no be any improvement just an expensive move.
if moving is not an option, and it seems that it isn't, you will probably be better served by putting your energies into emergency supplies and thinking about suitable routes out of the city should a serious life threatening event occur, not just vehicular routes but pedestrian ones too, forget about motorways, in the event of a serious happening they will end up as glorified car parks. there is more info in the archives of this forum plus look at the files on the main page.