No the gain is based on the difference between the purchase price ( in 03) and the sale price less a proportionate amount for the period while it was your ppr.
The determination is done on a pro rata basis. You bought in 2003, it changed from PPR to investment in 2007, if you were to sell in 2013 you would have to pay CGT on 50% of the TOTAL gain in price (10 years owned - 4 years PPR - 1 year grace).
Also, you may have to pay stamp duty clawback on the apt since you'll be renting it within 5 years of when you first bought it.