capital gains tax.

hi, we are going to move to spain permanently within the next year,  we have been advised to make ourselves a non resident in the U.K. first, move to spain THEN put our house here up for sale, BUT wait until it is sold before we apply for to be a spanish resident , apparently by doing it this way we can avoid paying capital gains tax on our U.K. property, (we already have a spanish property) IS THIS CORRECT, any replies would be appreciated.