CGT will apply for the period between May 2006 (12 month grace period) and when you sell. CGT will be calculated as a proportion of the total increase versus this, currently small, time period relative to total period owned.
Example always works best:
If you sell in May 2007 400K and you bought in May 2000 for 200K you then owe 20% of 1/7 of 200K = 5,714 less allowable expenses.
If you sell in Nov 2006 400K and you bought in May 2000 for 200K you then owe 20% of 1/14 of 200K = 2,857 less allowable expenses.