Consultants charging Merton taxpayers £2,000 a day have recommended the Civic Centre cash office should be closed to save money.
Critics claim thousands of residents unable or unwilling to pay council bills online or by direct debit will be badly affected by the proposed closure.
The move will save £80,000 a year although the council has said it is considering reducing the office’s opening hours as opposed to an outright closure.
But Merton’s opposition leader, Labour councillor, Steven Alambritis said: “Even if the hours are shortened, it’s absolutely meaningless if people can’t turn up to their town hall and know if the cash office is open.
“I’ve not had a cast iron guarantee that the hours will stay as they are or that the desk will even stay open. Thousands of people in Merton are financially excluded from the banking system.
“They don’t trust banks and they don’t trust direct debit. They want to sleep at night knowing their bills have been paid.”
Consultants also suggested an automated machine could be installed in Mitcham to reduce demand for the office, still allowing residents to pay council tax bills and parking fines.
Reducing opening hours of the office is listed in a document produced by the consultants as phase one in a two stage process of withdrawing the service.
But Merton Council’s deputy leader Councillor Samantha George said: "I would like to reassure residents that we have no intention of closing the cash office, although we are considering changes to the opening hours.
“To be financially prudent and to ensure best value for money, we regularly review ways in which we might be able provide our services to Merton's council tax payers in the most efficient way possible.
She added that residents can pay their bills by phone, direct debit, online or at paypoint systems in many shops across the borough.
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