The £20,000 annual ISA allowance is based on how much you contribute to the account per tax year, so making a withdrawal (or, if you have a Stocks & Shares ISA, selling your investments to Available Cash) doesn't deduct from this total.

For example, if you were to deposit £10,000 into an ISA and then withdraw it in the same tax year, you would still only have £10,000 remaining of the £20,000 limit to deposit in that financial year. If you wish to move money from your Moneybox ISA to an ISA with another provider, you should transfer the ISA rather than withdraw it.

Selling investments and holding funds as Available Cash does not affect your ISA allowance as the funds stay within the ISA wrapper.