How are withdrawals and replacements allocated within the ISA
Where a flexible ISA has current year subscriptions only, any withdrawals over and above the amount subscribed – for example, income or capital growth - can only be replaced in that ISA.
If you withdraw cash from a flexible ISA in a subsequent tax year, replacement subscriptions can only be made in that tax year back into the same ISA.
Flexible ISA withdrawals are deemed to be firstly of current year subscriptions, and secondly of previous year funds. Replacements are deemed to be firstly of previous year funds, and secondly of current year subscriptions.