It is reportedly going to get worse before it gets better! I did hear rumours from the banking world that the pound euro exchange rate might even get to 1:1 (I certainly hope not).
If only we had taken the decision to join the Euro when we had the chance.
Perhaps an option for all you who will be completing in June this year would be to keep your lump sum pounds in the UK for a while and take out a Spanish mortgage to pay the balance. I know it would cost more initially as you would be repaying each month (effectively) in pounds, but you would then be able to watch the exchange rate and pay off the mortgage with your UK pounds when the time was right.
Correct me if I'm wrong - but it may be worth considering rather than paying upwards of 10% more for your property.