I'm sorry to hear you're not enjoying Northumbria, but these things happen and choosing to take a step away is bold and a sign that you are taking control.
You probably know most of the good names already: King's, UCL, Queen Mary, Royal Holloway (although be aware that Royal Holloway is not in London itself, although it's close and has beautiful campus). But you should also consider Westminster which has a good social base and has a very good research profile indeed and is well regarded for Psychology and also Birkbeck, which many people forget about but which is a leading research base for cognitive science. The only problem with Birkbeck is that it is mainly a university for mature and/or part time students which may be a factor.
I have a King's bias and I have elsewhere on this site recommended King's new BSc in Psychology which is taught by the excellent Institute of Psychiatry, Psychology and Neuroscience. The IOPPN really is one of the world's great centres of mind science and this course is new, so competition for it may be less then otherwise expected. However, requirements are still likely to be rigorous. Talk to them. Talk to them all! Can any of your tutors/lecturers help you out if you have had a good first year academically? Please note that the better the institution, the less likely it is to accept transfers, as a general rule.
As for friendliness, the demeanour of Londoners generally should make no difference to your choice. Being a student in London will give you friends for life; that's what I have. But London is certainly expensive, so try for the best Uni you can in the hope of getting the best job.