How will the AEA and thresholds be applied to a mid-year CGT rate change?

Dear HMRC, Since the CGT rates are increasing in the middle of a tax-year, clearly two computations will need to be done for the different periods. My question is how will the AEA and thresholds be applied to the two periods? For a hypothetical example, if someone had income of £30,270, leaving £20k room at the lower rate and they had £50k gains before the 30th Oct and £50k gains afterwards, how will these gains be apportioned to the AEA and £20k lower rate threshold? Will the AEA and lower rate be applied to the earlier gains, the later gains, or some mixture of both? Thank you.

Hi ,
 

You can choose which transaction you want to use the annual allowance against for the relevant rate of tax to be applied on any difference. Our systems will be updated to reflect the date and rate changes to take this into account  . Thank you