If you had a joint account with either to sign then I do not think you need to get the authority of the other party.(posted 7910 days ago)Some banks will try to charge you £10 for each section requested, and each person reported.
If you want information about YOU held by the bank then you are entitled to it. And the maximum charge is £10 for your information.
If in doubt then call the Information Commissioner help line on 01625- 545700, they are busy but helpful.
Good Luck.