Red

Suppose I plan to buy a property in France as my principal residence and let out my UK house. Presumably my UK house then becomes a secondary residence and if I were to sell it I would have to pay Capital Gains Tax in either UK or France? My questions is - is the CGT avoidable? What if I made the UK house my principal residence prior to selling it - how long would I have to live there in order to avoid CGT? Can anyone help me with this please....? Mike