Selling uk shares bought when I lived abroad

I want to sell Santander shares bought in 1989 when I lived abroad. I returned to the uk in 2003. So to work out capital gains do I use the amount when I purchased the shares (I was abroad) or the value when I returned to the uk in 2003

Hi,
You would use a just and reasonable exchange rate in use at the time of acquistion in 1989, to work out your acquistion costs.  
This figure should be used when working out if there is a capital gain.  
For your convenience, there are exchange rates at:-
Exchange rates from HMRC in CSV and XML format and for older rates at:- 
Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2009.
You are free to use any of the supplied rates or one of your own choosing, such as from a recognised stock exchange.
Thank you