Some of Greece's biggest banks may have to shut and merge with their rivals, it has been claimed.
A European official told the Reuters news agency that Greece's four big banks - National Bank of Greece, Eurobank, Piraeus and Alpha Bank - could be reduced to just two.
European leaders are meeting on Sunday in a bid to strike a financial aid deal with Greece.
Britain cannot be "immune" from the fall-out from today's Greek referendum, George Osborne has warned.
"I don't think anyone should be in any doubt - the Greek situation has an impact on the European economy which has an impact on us," the Chancellor told BBC1's The Andrew Marr Show. "We cannot be immune from these developments.
"Whatever Greece decides, Britain is prepared," he said. "We have the plans in place for whatever the outcome is."
David Cameron will chair talks with Mr Osborne and Bank of England Governor Mark Carney tomorrow morning to assess the impact of the poll, which could see Greece become the first country to be forced out of the euro.
The Greeks have voted to reject the austerity terms demanded by eurozone creditors - so, what happens next?
Greeks have voted to reject the terms of an international bailout, putting it on the brink of a eurozone exit.
Greece's controversial Finance Minister Yanis Varoufakis has released a defiant statement of resignation entitled 'Minister no more!'