Hi mailgvuk1,
Income and Capital Gains Tax are charged in the UK, using the arising basis.
As a UK tax resident, by default, you are taxable on your world-wide income / capital gains using the arising basis, regardless of whether you remit the income or gains to the UK or not.
Even if all transactions ocurr outside the UK on foreign exchanges, the gains are taxable in the UK and should be declared on a Self Assesment tax return.
If you are UK resident but not UK domiciled, then you have the opportunity to use the remittance basis instead.
Please have a look at the guidance here:
Residence, domicile and the remittance basis: RDR1
As this is not always the best option.
Thank you.