have just had a chat with the senior FX traders in the treasury of the bank where I work
the unanimous message I am getting (from people who have assets overseas) is that you do not have to pay CGT on standalone FX gains. It makes sense that you would not, since the process would be unworkable - everyone would have to declare every sum of money they transfer between the UK and Ireland - thousands of transfers a day I suspect! Also, what happens if you incurred a loss? Then you would be in really complicated territory of getting tax credits!!
If the FX gain is on the back of a sale of an underlying asset, then the gain would be added to the profit of the total transaction, and taxed appropriately. the FX gain would not be stripped out for CGT purposes.
The situation you are in seems like a grey area. It could be argued that the inheritance is a transaction onto which the FX gain should be added in the same was as if you had sold a UK house and were converting back to Euros. However, since you have presumably already paid some kind of inheritance tax (a process about which I know nothing), you should at this stage just be able to transfer the money into Euro as a standalone FX transaction, which is not liable to CGT