How can Theresa May sell Brexit at the G20, where she has few friends among a group of protectionist nationalists?

For some reason, Theresa May has a habit of sometimes looking very lonely in news photographs, much to the glee of the headline writers and the satirists. Perhaps her media handlers aren’t attentive enough to the “optics”; maybe it is because of a certain innate personal shyness; and sometimes it must be the result of the all-round embarrassment of Brexit.

As she arrives in Buenos Aires for the G20 summit she may also find things there a little difficult socially. Downing Street has already put out the line that she is not scheduled to meet for any fringe or bilateral sessions with Donald Trump. Apparently and understandably she is disappointed, to say the least, about Mr Trump’s intervention in the Brexit debate, his line about the withdrawal agreement being “a great deal for the EU”, making the lonely task of selling her unloved compromise just that bit more difficult.

The time when Ms May was led by the hand around the White House rose garden as the first foreign leader to be granted the honour of meeting the new president in Washington seems long past indeed.

Nor will she have much to say to the Russian president, Vladimir Putin, for obvious reasons. Perhaps a day will come, under different circumstances and leadership, when Britain and Russia can repair their relations, but with the murderous activities of Russian agents on British soil still so recent, this little cold war is not ready for a thaw.

And, if she turns to Pedro Sanchez of Spain for a chat, then she’d better not mention Gibraltar, or the fact that Spain, the 15th largest economy in the world, is only attending as an “invited guest”, rather than as of right, for the usual reasons of geopolitics.

The one leader the prime minister probably should not be taking tea with is the crown prince of Saudi Arabia, and de factor ruler, Mohammad bin Salman. Enough is already known about the events that led to the murder of the blameless journalist Jamal Khashoggi to put such a friendly meeting out of the question. Indeed, the prince might count himself lucky not to be arrested under international law once he descends onto Argentinian soil. Even if she is hard up for friends these days, and surrounded by authoritarian populists from Italy, Turkey, India, China, Indonesia and Mexico, she should not have agreed to this meeting.

In fact, the G20 summit is a striking reminder of how much global politics has shifted in recent years, and how ill-fitting this new wave of protectionist nationalists are to a body with the ostensible primary aim of making the world economy run better. From Italy’s Matteo Salvini to President Trump to Recep Tayyip Erdogan, we find at the G20 few leaders who even believe in a free-trading globalised rules-based world economy, let alone have any interest in cooperating in economic and financial policies. “America First” is joined by “Italy First”, “Turkey First”, “Russia First” and even “Brexit First”. It is a hostile environment for consensus and for the post-war system of international organisations, of which the G20 was a relatively late entrant.

Indeed, the rest of the usual G20 agenda – climate change, development and international aid and low-key attempts at peacemaking – also seems doomed to failure. Within the G20, trade wars have broken out between some of its most prominent members, including the US, China, the EU, South Korea and Japan; Mexico and Canada exchange insults with America; and proxy wars are being waged between Turkey, Saudi Arabia, Russia and the US. Russia is at war with Ukraine, friend of Germany and America.

It is all a sorry contrast to the G20’s finest hours in 2008 and 2009, when heads of government, finance ministers and central bankers organised a series of high-pressure emergency meetings to deal with a financial crisis that threatened a great depression. Led by Gordon Brown and Barack Obama, initiatives were taken to maintain free trade, boost the major economies – the bulk of world GDP – simultaneously, and for all nations to adopt a mutually reinforcing comprehensive system of support for their collapsing and deeply interconnected, banks. The G20 saved the world.

While the effects of the crisis are still with us, and it heralded in an era of austerity, recession and rising poverty in advanced economies, the very worst of what might have happened was averted. It was done through a combination of broadly shared values, strong leadership and, above all, a sense of staring over a precipice.

The financial crisis also, after a lag, bequeathed today’s breed of nationalist leaders, of which Ms May, as the willing high priestess of Brexit, can to that degree also be counted. They will agree to very little over this weekend – which should surprise no one.

What is much more terrifying is the thought of this group having to take concerted intelligent action if some new existential crisis comes to threaten the prosperity of their citizens, and those of the many poorer nations unrepresented in their discussions. The irony, or course, is the very policies pursued by Mr Trump, Mr Xi, Mr Putin and the rest of them could well precipitate just a such a combination of economic and geopolitical instability. In 2008 and 2009 the G20 could, and did, save the world; the same cannot be thought today.

It is reported that Ms May will be taking the opportunity to tell her fellow leaders that Brexit will be good for the world economy and “play a full and active role on trade on the global stage” after Brexit. Given that the UK represents just 2 per cent of global GDP, that may not be the most impressive claim to brandish around the conference table. The increase alone in the size of the Chinese economy over the next three years or so will be larger than the UK’s entire national income. The world has bigger fish to fry than Brexit.