These prices are sustainable only in the short term. Q/E has pumped a lot of money into the property sector and in London in particular this is having an effect. Foreign money has poured in also compounding the problem because UK property is perhaps the least regulated in the world and capital can flow freely in and out (generally). Foreign money has poured in from growth economies that still lack at this time sound legal systems to protect wealth creation. Money is parked here in property to protect it more than produce an income.
Residential portfolios yield very little in income - rents are a low comparative yield to values. In a perfect market this is unsustainable to investors. It is normally possible to make 6-7% pa long term post inflation returns on the stock market, so in theory investing there should in the longer term outgrow property prices. Remember that corporate earnings underpin wages and investment returns which in turn underpin house price growth. If business is not performing then house prices cannot. This is why stocks and shares, the very essence of where we spend 90% of our money, have historically outperformed property by around 1%.
The value of anything is in the personal satisfaction that it gives or the income it can produce. Chasing property on the basis "it will always go up" is a fool's dream and capital growth is only someone else's perception of future incomes. As most people are not lottery winners and cannot afford to outbid at any cost another purchaser for the 'chocolate box' cottage, then houses are generally underpinned by UK earnings. If earnings do not grow, then house prices will fall, all things equal and particularly if interest rates rise - which they will eventually - and also particularly if earnings growth is not allowed to take place (yes - allowed - because it is in Osborne's hands to unfreeze public sector pay and in Carney's hands to create some inflation so that growth and debt reductions in real terms take place).
I forecast a more structural fall in house prices in due course. When - I don't know, but in the current generation. We had a soft landing in the 2008+ economic crisis due to low interest rates and Q/E. That will not last for ever.
There are a lot of generalisations above, but I do not have time to post much more. For now I would get some even balance and try to invest in broad stocks and share ISAs for a few years if you can. Don't get despondent, we have seen these cycles before but for different reasons and it always comes back to the market.