very interesting thread, as I am just about to hit the market, sell the current flat the missus owns and buy a house together.
Currently i think the flat mortgage is about £400/month - but after all bills, petrol etc have been paid, i'm still managing to save nearly £400 a month - so I THINK we can safely double our mortgage costs and still survive. On the plus side we'd be moving closer to my work, so i wouldn't be paying £400/month in petrol, so could probably use that money for the extra bits for the house.
From so much advise and comments from others, it seems like we're going to need to move soon, as they recon a largeish increase is still due to hit house prices in the South soon.