Greece has threatened to seek a court injunction against the EU institutions, both to block the country's expulsion from the euro and to halt asphyxiation of the banking system.

"The Greek government will make use of all our legal rights," said the finance minister, Yanis Varoufakis.

"We are taking advice and will certainly consider an injunction at the European Court of Justice. The EU treaties make no provision for euro exit and we refuse to accept it. Our membership is not negotiable," he told the Telegraph.