Hi mona lee,
No, you will need to convert your acquisition costs and disposal costs to pounds sterling, to work out any gain.
From this, you can also deduct your buying and selling costs:
CG15250 - Expenditure: incidental costs of acquisition and disposal
Regardless of whether you have any Capital Gains Tax to pay, the fact that you have a foreign gain, is Self Assessment criteria.
So you will be required to record the disposal in a Self Assessment tax return.
Thank you.