That's about the benchmark for graduate salaries in London. When you are a new graduate you don't know much and so the firm is not going to go overboard, they will pay the going rate. Most graduates in London live in houseshares similar to students, yes that might suck if you had ambitions of having your own studio flat or whatever when you graduated but if you want that you will have to move to another city (you can rent a nice riverside studio in Leeds / Manchester on a graduate salary).
The one good thing about rents being so high in those houseshares in London, is if you are sharing with a group of others in a place where you're paying £800 a month each in rent, it's a fair bet you are all on graduate jobs. You aren't likely to get a layabout in the group who just wants to stay up all night getting hammered and being noisy all the time, because they won't be able to afford it.
If you want to enjoy a better lifestyle you just have to be good and successful in your career. Your firm will work out pretty soon who is really needed and who isn't, and they will promote the ones who are really good.
On a salary of £45-50k which is perfectly reasonable in 3 or 4 years in most professional graduate schemes, if you get promoted, you can live a bit more comfortably in terms of renting in London however you might still struggle to save for a deposit so buying in London isn't going to be a go-er unless you are in a couple both on that sort of salary with some significant parental help.