Thanks for your response
If the Swiss capital gains tax is less, then yes you will on the initial gain have a remaining liability in the UK.
But from the initial gain (so sale price less purchase price) you can deduct
1) The costs to purchase - such as legal fees
2) The costs of any major improvements to the property
3) The costs to sell - such as legal fees
4) And have any tax reliefs considered, for example had this ever been your main residence in which private residence relief would be due on part of the gain, and had this not only been your main residence but also let out (and rental income declared to HMRC) then private lettings relief.
Then the first £10,600 is capital gain free, as this is the annual exemption allowance, and finally any gain remaining is liable to 28% capital gains tax.
Then you would claim the Swiss capital gains tax suffered, and only then, should there be a remaining liability then this is what you would pay to HMRC for the UK capital gain tax position.