I think you mean this is the form from the bank when you open your account. The bank needs to know if you are resident or non resident for your account. If you are resident they would declare this to the tax authority in Spain. You will be declaring “no residente” meaning your tax affairs are back in the UK. The bank should send you this from every 2 years for you to renew your non resident or resident status.
However, the Spanish bank are required to tell the Inland Revenue here of any interest you receive but if this happens or not im not really sure.
Dont forget that even if you non resident and not renting you are supposed to pay the assumed rental tax that the Spanish tax authority wants.