None! One of the great things about ISAs and JISAs is that so long as you stay within your deposit limit*, there are no tax implications to worry about! You can make deposits and withdrawals without needing to report anything on a tax return!
Therefore, if you only hold an ISA and/or a JISA there are no tax implications for you to worry about!
*For the 2020/2021 tax year, the ISA allowance is £20,000 and the JISA allowance is £9,000.