When I was in London one of the places I lived in had damp, but that was a basement flat. The other place I lived in (ground floor flat) was fine though, and that was just round the corner.

Not sure that London is more prone to damp than anywhere else though, unless it's something to do with a larger concentration of older buildings or something (assuming older buildings are more likely to have such problems, I am not sure)?

We live in a pretty old building which seems to have no insulation whatsoever. And we're on the bottom floor (ground floor, kind of below street level at the back!).

Of the four places I lived in while in London, only one had damp...

We have little bits of damp, but it's because the brickwork needs repointing; I don't think London is any better or worse than anywhere else.

Depends completely on the building, the damproofing & wether or not there are any leaks, debris above the dampcourse and so forth! Modern buildings can/tend to be prone to condensation due to lack of ventilation. (Or when people block vents off, etc:)

None of my London flats have had damp (all ground floor, a nice place in SW19, ex-council places in E2 and N1). My gf's place does have damp, in the bathroom, but that's a piss-poor conversion job on a terrace / back-of-shops house. I think the mould is just from condensation rather than actual rising damp.

If you've got black mould on your walls, take photos, then bleach it and scream at your landlord until they do something about it - that stuff is really bad for your lungs.