Double Interest on ISA Transfer - Tax Implications

I had a Cash ISA transfer from Bank A to Bank B initiated in July. However, due to a bank error, the transfer was unsuccessful. Despite the failed transfer, Bank A continued to pay interest into my account from July. The transfer finally completed in February, and Bank B is now calculating the interest I would have earned with them since July. As a result, I have received interest from both banks for this period. Do I need to pay tax on this "double interest"? If so, how do I calculate the amount owed?

Hi questionsam112,
As it is double tax, you will need to decide which one is not to be classed as ISA interest and to form part of your personal savings allowance.
If under £1000 is received from all non ISA accounts in they year, no tax wil be due.
Thank you.