Have you considered moving out of London? (or are your jobs/industries key to London).
I'd hate the thought of spending 300+k for a 1 bed flat in zone 3 (someone told me that's how much it is :X)
It's on the cards however my area of work is very specialised and is only really available in London. I'm considering taking a slight de-tour with my career so we can move somewhere cheaper but I haven't worked out the finances yet as I'll likely take a significant pay cut.
We currently live in Zone 3 boarding on 2 and the 300k is about right! Our rent is £1500 a month for a two bedroom duplex flat. It's a bit soul destroying throwing that money away every month but it's the reality of living in London.