Greek voters go to the polls today in a crunch referendum on the country's debt deal, with the impact set to ripple across the rest of Europe whatever the result.
The nation's left-wing government has let it fall to its people to decide whether to accept an austerity package put forward by international lenders in return for a further bailout from the eurozone rescue fund.
Banks have been closed all week to prevent a run driven by savers withdrawing cash amid uncertainty about whether the country will crash out of the euro, after falling into arrears with the International Monetary Fund (IMF).
Prime Minister David Cameron has said the poll will essentially amount to an "in/out" vote on Grexit - whether Greece should leave the eurozone.
Meanwhile Chancellor George Osborne has said: "I don't think anyone should underestimate the impact a Greek exit from the euro would have on the European economy and the knock-on effects on us."
Rallies have taken place across the UK over the issue, while British tourists travelling to the country have been advised to take cash with them and be wary of their personal safety.
Many Greeks living in Britain have returned there to vote while those who are unable to return at short notice say it is "always on their mind" as their concern for family members grows.
Greek citizens living in the UK could only take part in the referendum if they return to Greece to cast their vote.
Rallies have taken place in London's Trafalgar Square, Leeds, Liverpool, Bristol and Edinburgh, with another today in Manchester.
Prime minister Alexis Tsipras, who has promised to ease austerity after six years of recession, called the snap referendum on the proposals from the creditors - the EU, European Central Bank and IMF - which would impose further potentially painful economic reforms.
Mr Tsipras, 40, is gambling the future of his government on the poll, insisting a No vote will strengthen his hand to negotiate a third bailout with better terms.
He is seeking to reduce the country's 320 billion euro (£227 billion) national debt and make payments more sustainable.
If he loses, he has strongly indicated he would step aside.