Hey, @IntInv - I’ll be happy to clarify this for you 
The ISAs that we offer are flexible, meaning you can withdraw funds and replace them within the same tax year without affecting your annual ISA allowance. So, if you withdraw £20,000, you can re-deposit that amount and it won’t count towards your £20,000 annual limit, as long as the funds are returned to your ISA within the same tax year.
If you withdraw that amount and haven’t utilised any part of your ISA allowance for the 2025/2026 tax year, this means that you can then deposit a maximum of £40,000 in one go - the £20,000 that you withdrew and are now paying back, as well as another £20,000 that will utilise the available allowance for the current tax year.
No, the source of the funds doesn’t affect the flexibility. As long as you re-deposit the withdrawn amount within the same tax year, it won’t impact your annual ISA allowance.
We strive to process withdrawals as quickly as possible - while it may take up to 3 business days, some transactions take less time depending on the method used.
Don’t hesitate to let us know if you have any further questions - we will gladly help.