Many thanks for your reply. 1990's it should be!
Your reply reminded me that there was an arrangement that if we held the shares for 5 years they were free of tax. However, I don't have paperwork from the time and the company is no longer based in Ireland. The administration of the scheme was dealt with by an Irish company so I will see if I can locate any paperwork from them. However, my priority is to ensure I am clear with Revenue.
Again, many thanks for your reply.