Mr Justice Andrew Smith may take months over his judgement
The judge hearing the High Court test case on bank charges said his eventual ruling should help resolve thousands of claims pending in the county courts.
But Mr Justice Andrew Smith, concluding on the 14th day of the hearing, said he had "no idea at all" when he would be able to deliver his judgement.
"I have a great deal of work to do before I make my judgement," he said.
The case has been staged to decide if bank overdraft charges can be regulated by consumer contract legislation.
While the hearing has focused on existing terms and conditions that banks apply to their current accounts and overdraft charges, thousands of claims for the return of overdraft charges are still on hold in the county courts.
Most of these were originally lodged by bank customers who were complaining about their bank's previous terms and conditions.
Many such claims were frozen last summer when the banks, the Office of Fair Trading, the Financial Services Authority, and the judiciary decided that a test case was need to resolve some of the legal issues involved.
Mr Justice Smith said he hoped his eventual judgement would give some guidance to county court judges.
"There is every indication that my findings will translate to the historic terms," he said.
"That could mean a decision on the historic terms in very short order - maybe within a month [of my decision]," he added.
The prospect of a decision that goes against them has always been worrying to the banks as it might jeopardise about £3.5bn a year that they currently derive from overdraft charges.
In court, several bank barristers expressed unease that Mr Justice Smith's eventual findings might leak out in the time between him circulating a draft ruling to the parties to the case, and handing down his final public decision.
"The key point is to ensure there is no breach of confidentiality on the draft judgement," said Mr Ali Malek for the Abbey bank.
Mr Justice Smith said he was "deeply troubled" by such a scenario.
He then decided that his draft judgement would be sent out only to a "very tight circle" of named lawyers for the OFT, seven banks and the Nationwide building society.
Earlier in the proceedings the barrister for Lloyds TSB, Mr Bankim Thanki QC, had expressed concern that once the judge's decision was known the banks would be inundated with calls from customers asking about their claims.
He had asked that the draft judgement be circulated on a Friday to give his bank time to digest it over a weekend and to prepare to respond to its customers.
Now, Mr Justice Smith has decided that he will probably give the parties to the case just 24 hours to respond to any typographical or factual errors.