Tax on sale of foreign investment portfolio

I have an investment portfolio held in an EU country which I am considering selling/closing. Would the resulting proceeds need to be entered into my UK tax return (even if the resulting funds remain abroad) and if so, under which sections/boxes of the self assessment document ? Thank you

Hi,
The UK charges income tax and capital gains tax using the 'arising' basis, on world-wide income, even if it is not remitted to the UK.  
Any individual resident and domiciled in the UK, or resident but not domiciled in the UK, is taxed on the arising basis by default, which means the foreign income of UK residents is charged to tax in the year in which it arises overseas.  
For individuals, who are resident but not domiciled, they can elect to use the 'remittance basis.  
Please see further guidance on the  remittance basis:
Residence, domicile and the remittance basis: RDR1
As your portfolio is an asset, you may be subject to capital gains tax on any gains arising from the disposal.
Thank you.