The risk in this process is entirely yours.
Any income or gains arising outside the UK, in a tax year before you became resident, is not taxable in the UK.
There is a possibility that your income/gains arising in the tax year that you became resident in the UK, may be taxable in the UK.
To find out if this is the case, you will need to review your residence position and whether split year treatment applies.
Have a look at :
Residence, domicile and the remittance basis: RDR1
and then the statutory residence tests at :