David Cameron has signalled that the election of a pro-bailout party in Greece has done little to resolve the long-term problems within the eurozone, suggesting Europe faces "perpetual stagnation" or a break-up of the single currency.
Despite the New Democracy Party narrowly winning the Greek general election on Sunday the Prime Minister will use a speech later on Monday to say the crisis in the euro area is at the top of a list of "five big threats to the global economy".
He will urge the leaders of the world's biggest economies, gathering in Mexico for the G20 summit, to take "bold steps" to restore growth, and will warn against "backsliding" on trade protectionism and reforms to financial regulation.
A failure to follow through on pledges made at previous summits to reform the banks would leave the world exposed to a repeat of the 2008 financial crash, he will warn.
No corner of the world is safe from the threats of the eurozone instability, sovereign debt, low growth, protectionism and failure to regulate the banks, the PM will say.
"These five threats are very real. And let's be clear - in a global economy, they threaten us all."
The G20 summit in the Pacific resort town of Los Cabos is taking place at a time of heightened tension in the world economy, sparked by yesterday's elections in Greece in which pro-bailout Conservatives came first. The vote was widely seen as a referendum on whether the country will comply with austerity measures imposed in return for the multi-billion euro bailout of its stricken economy.
Results from Greece were trickling through as Mr Cameron flew out of Heathrow on Sunday night, and he is expected to keep in touch with London by satellite phone during the 13-hour flight to monitor the progress of attempts to form a pro-euro coalition government in Athens and the all-important reaction of the markets.
Eurozone leaders including German chancellor Angela Merkel, French president Francois Hollande and Italian PM Mario Monti were expected to delay their departure until the morning in order to be in place as the shape of the new political landscape in Athens becomes clear.
Speaking to the B20 business summit in Los Cabos shortly after his arrival, Mr Cameron is expected to renew his call on the 17 eurozone states to take the steps towards closer fiscal and financial integration which he believes are necessary to restore stability.
He will call on "core" members like Germany, as well as the ECB, to "do more to support demand and share the burden of adjustment", warning that central banks cannot afford to "stand on the sidelines" in the current crisis.
"The reality is that there are a set of things that eurozone countries need to do," the PM will say. "And it's up to eurozone countries whether they are prepared to make the sacrifices these entail.
"The challenge is one of political will as much as economics. Of course these things are difficult to do, but just because these things are difficult does not mean we should not say them.
"If the eurozone is to stay together then it has to make at least some of these difficult decisions.
"The alternatives to action that creates a more coherent eurozone are either a perpetual stagnation from a eurozone crisis that is never resolved or a break-up caused by a failure to address underlying economic fundamentals that would have financial consequences that would badly damage the world economy, including Britain."
Mr Cameron will say that the UK has a "clear vision" of the "stable, growing, competitive and dynamic" world economy, powered by trade and financed by strong banks, which it wishes to create.
But he will warn of five threats to this vision: instability and contagion in the eurozone; debt and the "muddle-headed" belief that indebted countries can spend their way out of crisis; the failure to deliver the monetary activism and structural reform needed to deliver sustainable growth; 1930s-style protectionist barriers to trade; and the failure to complete long-term banking reforms.
With its members representing 90% of the world economy, the G20 is "the right forum to work together to deal with these threats", he will say.
But he will warn that G20 leaders need to show "courage, resolve and political commitment", adding: "There can be no room for timidity in meeting these threats, no ducking the essential action on fiscal discipline, monetary activism and structural reform and no backsliding on the hard-won gains of previous summits.
"For the G20 to give in to self-defeating protectionism or to water down the tough new commitments on financial regulation would be unforgivable."
Former chancellor Norman Lamont said Syriza's failure at the ballot box had probably delayed a "very bad crisis" but warned "nothing underneath has changed very much".
Mr Lamont told Sky News: "I think there will be a certain amount of relief that what some people would see as the worst outcome has been avoided and you are not going to get confrontation between a Syriza-led government and the eurozone.
"But I think in reality nothing underneath has changed very much. Very few people believe Greece is in a tenable position for the long term but at least an immediate very bad crisis has probably been put off."
Britain is pushing for G20 states including the US, Russia, Indonesia and South Korea to complete the implementation of the Basel III requirements on bank liquidity and leverage agreed following the 2008 crisis.