Selling our UK home

Hi. Have just joined Survive France as it looks like a really good site and maybe someone on the forum will be able to solve our dilemma. I’ve just read this morning about the recent changes in CGT tax rules in France which apply to the sale of second homes after 1/2/12. We are resident in France and have declared our french property as our primary residence since 2009. We were planning on selling our UK home next year, and had understood that we would not be liable to any CGT as we had owned it for more than 15 years. However, under the new regulations, CGT is now payable on property owned up to 30 years. All of the information I have found on the web relates to selling houses in France and I am seeking advice on selling our UK home which we have had for twenty years. That is, how do the French authorities calculate the CGT on a foreign (UK) property? Hope someone will come up with some good news for us. Thanks.