Are we liable for Capital Gains Tax on our sole property in the UK?

So long as you sell it within 3 years of moving out there will be no question of UK CGT on it. If you sell after that time there could be CGT if you decide to come back to the UK in the next two years or so. It is not enough just to be non-resident when you sell: you have to remain non-resident for at least 5 complete tax years after a sale.