Europe must be "prepared for the worst" as the Greek crisis enters a crucial period, Chancellor George Osborne has warned.
After a meeting in Luxembourg of eurozone finance ministers failed to make a breakthrough, Mr Osborne issued a last ditch appeal to the Greek government to do a deal with its creditors to prevent it falling out of the euro.
There are signs that Greeks are taking their money out of banks in ever-increasing amounts because of the uncertainty over the country's future as a deadline for Athens to reach an agreement over its bailout loomed.
An EU official said two billion euro (£1.4 billion) had been withdrawn in the last three days.
"Money is going out of the Greek banks faster than at any time before," he added.
Mr Osborne said Treasury officials were working to complete preparations to protect the British economy from the effects of a disorderly "Grexit" by Athens from the single currency.
"We have entered the 11th hour of this Greek crisis, and we urge the Greek government to do a deal before it is too late. We hope for the best, but we now must be prepared for the worst," Mr Osborne said.
"In the United Kingdom we've taken the measures to increase our economic security so we can deal with risks like this from abroad. And clearly now we must go on and complete that plan."
The Chancellor is in Luxembourg for a full meeting of EU finance ministers following yesterday's eurozone group meeting.
With time running out for a Greek deal, an emergency summit meeting in Brussels of the eurozone leaders on Monday may offer the last chance of an agreement.
The current Greek bailout expires on June 30 when Athens is due to repay 1.6 billion euro (£1.15 billion) to the International Monetary Fund (IMF).
The head of the IMF, Christine Lagarde, has warned the left-wing Syriza government of Alexis Tsipras that if it fails to make the payment it will be in default and will be disqualified from receiving further IMF funds.
Finnish finance minister Alexander Stubb warned "right now it's touch and go" whether a deal can be brokered.
French finance minister Michel Sapin said it is becoming a matter of urgency to find a solution to "this situation that is becoming unbearable".