Hello, my name is Tony. I can answer this for you.
Have proceedings been issued, and if so, how much are you being sued for?
Then you need to make an application to the Court for an order that he disclose his bank account statements to you. This is necessary as the Court usually only does this automatically for claims for more than £10,000.
The application needs to be made on Form N244, which you can get here: http://www.hmcourts-service.gov.uk/HMCSCourtFinder/GetForm.do?court_forms_id=484
It asks you what order you're asking for, and you need to say you want an order for "specific disclosure of the [defendant's] bank statements."
You don't need them - he has to provide the relevant bank statements - that is his obligation under such an order.
You need to fill in the back of the form (Section C) and explain to the Court why the statements are needed for your case.
Then the Court will decide whether to order them to be disclosed to you. If they are relevant to the outcome, it is likely to order this.
Does this answer your question this evening as to how to get the bank statements?
Is there anything you would like me to address about this for you that I haven't?