If you're looking outside of London, York is certainly one to consider. Loughborough is sadly not the leader it used to be, thanks to a number of strange organisational decisions. Nottingham is also excellent, but is more focussed on the computer science side of HCI. In general, the CS side doesn't give the same range of potential jobs afterwards.
I used to be the Head of the Centre of HCI Design at City - we certainly had excellent job prospects (the last thing I knew, the best in the UK), but many of the degrees do well. The team at York are strong, and Paul Cairns is a genuinely friendly and thoughtful lecturer, who I've heard consistently positive things about.
All the best,
George