I know london is more expensive than others places in the uk so I wonder what is a good stipend for a phd in London??thanks

London is more expensive than the rest of the UK (particulalrly accomodation).

A good stipend would be at least 12,000 pounds a year as accommodation will eat up most of that.

15000 not less

with 12000 you will not be able to enjoy the luxuries of London, but will be able to aford the basics, i.e. accomodation, food and a friday night out