there is a real risk that the UK property market bubble would have been even bigger if we had been in the Euro for the last few years, given the lower interest rate in Eurozone. I have no truck with those who are against joining the Euro for "little Englander" reasons, but there are good economic reasons for the UK not to be in the Euro zone at the moment. If the UK had joined the Euro at 1.50, the UK would be an even worse state now, with a fixed overvalued exchange rate and no control over interest rates. The devaluation of £ will be one of the factors that gets the UK economy going again.
There will be a right time to join the Euro, but it isn't now, and it wasn't in the last few years. In the meantime, this is a massive test of the Euro, and its one interest rate fits all. European economies have clearly not converged, and places like Ireland and Spain require a somewhat different interest rate than Germany right now. Ireland and Spain (and several others) need an economic stimulus - they can't do it through interest rates, they can't do much fiscally due to budget deficits, and they can't devalue their currency - they are running out of economic tools to manage the economy