In which part of London do you get an apartment for £425? I had the impression that you have to pay at least 3x that amount to get a reasonable apartment in a somewhat central place.
There's plenty of low cost housing in London, it's just that you won't be living anywhere near the bits of London that you're thinking of ;) I used to live in an old edwardian house in Greenwich, it's a nice area and doesn't take too long to get into the centre.
Greenwich/Lewisham area in Zone 2. It depends, my house is pretty low standard though.
I pay a similar amount sharing with two friends in Clapham/Balham. It helps that we've been in the same place for 4 years so the rent hasn't gone up too much over that period.
I pay ~£1000 mortgage in a reasonable area within 15 minutes of centre. Renting is more expensive.