My friend agreed to sell a property he owned to his son who was renting the house in 2015. The sales price was agreed at 2015 level. He now wishes to draw up sales contract and complete the sale legally. The reason the sale was not completed at the time was that his son had to move abroad with his job and the sale was delayed. From a CGT & a CAT perspective can he use the 2015 selling price agreed or must the SP be at 2017 price level?