No no no! London would be massively more expensive than Durham when you include tube costs, etc. Also, most London unis don't guarantee accomodation. I know a guy at Goldsmith's living out in London - he said, "it's fine so long as you don't leave your house, EVER." [Even though people at London unis get higher loans.] Think about how expensive nights out in London would be - Durham is cheap as chips and we have all these student bars!
HOWEVER, Durham is very expensive compared to most non-London unis.