Dude ... you can "get by" on £70K in London. Most people get by on MUCH less. £70K would get you a nice rental flat, eating out anytime you like and still saving about £20-30K a year. And that's if you're single, if you're sharing expenses you could save more.
"get by", seriously?
The median salary for London is £34,473 (2015 data).
With that salary you could easily save £1500 a month