THE biggest sporting caravan in the world lumbers on. The dogs continue to bark even as two of its most illustrious passengers have fallen off, returning home to cries about their respective worth, their failure and their long-term future.

The World Cup continues, but for Lionel Messi and Cristiano Ronaldo life returns to the routinely febrile atmosphere of extraordinary fame, merciless scrutiny and the seemingly eternal argument about who is better and, indeed, if either is the greatest footballer of all time.

It is a debate that can be dismissed as narrow, even restricted to a precise constituency. But it testifies loudly to a truth of the world in which we live. Trump v Liberal, Yes v No, Brexit v Remain, Leo v Cristiano: this is a planet where nuance has largely disappeared into the atmosphere and where rational doubt about the validity of a set of beliefs has become conspicuous by its absence in many.

“We are living unfortunately in a world which I would classify as disordered, a world which is confrontational and Manichean. People take one side or the other,” says Jimmy Burns, who has written a dual biography of the players (Cristiano & Leo, MacMillan, £16.99.)

“I called it this rather than ‘Cristiano v Leo’ or ‘Cristiano or Leo’ as I wanted to try to convey my own sense of why these two players on their own terms – and they are very different terms – deserve our respect.”

Messi, of course, is the Argentinian talisman of Barcelona whose slight frame carries not only the burden of his nation’s hopes but complements the belief that genius can come in the smallest of packages. Perceived as shy and introverted, he is placed on the opposite end of the spectrum of the mighty, arrogant Ronaldo, star of Real Madrid and leader of Portugal. The debate about their relative worth has polarised. Mild criticism of one is taken as unbridled support for the other.

“Football can be very tribal and people get drawn into this political battle. The millennials conduct debate and issue their views largely thought social media. This is quite visceral in terms of people taking sides. Twitter accentuates that.”

Burns, who has written a biography of Maradona as well as histories of Barcelona FC and Spanish football, adds: “As a football fan what we should be appreciating is the genius of two players who have given us a great deal of joy.”

The careers of both players have placed them in an unprecedented spotlight as regards football media, yet neither have used this opportunity to declare anything of political substance.

“Messi has consciously distanced himself from Catalan politics,” says Burns of the fervent debate that has dominated the agenda in Iberia. “If you compare him with Johan Cruyff and Pep Guardiola, two icons of Barca history who clearly identified themselves politically with Catalanism, then Messi has deliberately avoided being drawn into the politics of the culture. I think that is admirable because I think it engages with a more global audience. People respect him for the way he plays rather than what he says.”

He adds: “You wouldn’t call Ronaldo political in the normal sense. But both understand power and how to use it.”

Messi and Ronaldo wield extraordinary influence at club and international level. There were reports, substantiated by photographs in the tunnel and recordings of pitchside conversations, that Messi was heavily influencing, perhaps even selecting, the national side at this World Cup.

“The power they have within their clubs is earned by merit and is a product of their own achievements,” says Burns. “They have won the respect and the right to have a say in the teams because they are way above the level of the other players. The teams are to a great extent dependent on their performance.”

This has been to the advantage of Ronaldo, who is seen as a player who has towed Portugal to success, particularly in light of their restricted resources, and to the detriment of Messi, who has been criticised for not dragging Argentina to a World Cup in the manner of Maradona.

Their power is not used politically but it carries a substantial economic heft. Ronaldo, for example, has 74 million Twitter followers. “They lead that huge monster of football marketing. They are slightly different in the way they pursue their financial goals but have used and adapted to the modern world brilliantly.”

Burns has soberly distilled the spectacular. The dual biography eschews partisanship and has proper scrutiny of the foibles, fallibilities and failings of the protagonists. It stands, though, as a celebration of two extraordinary sporting talents.

“It is a deliberate attempt to write a dual biography, to be even-handed,” says Burns. In the schism of a world seemingly devoted to the cult of Messi or the religion of Ronaldo, he says: “I am an agnostic. I use the YouTube test. As part of the research for the book I had to look back on their goals. You would start watching one goal and two hours later you were still watching.”

But does he believe Messi and Ronaldo are better than anything that has come before? More deserving of the title of greatest of all time than Pele or Maradona?

“I believe that title is between them,” he says. “You have to appreciate their greatness in the context of the modern game. They not only play sublime football but in an atmosphere of extreme pressure that never existed in the time of Maradona or Pele. The intensity of the game, the number of games they have to play, the competitive environment dwarfs anything that Pele or Maradona had to face. It is a different ball game.”

He adds: “I entered the project in a very divisive world, in a very conflicted and confrontational world. The reality is that within modern football you have these two geniuses fighting it out to be the best in history.”

Ronaldo, at 33, and Messi, at 31, have limited time to press their cases. The argument, though, threatens to be eternal.


Left and right wingers ... The politics of football

Socrates: The Brazil footballer who illuminated the 1982 World Cup was a socialist who bravely espoused democracy in the time of military junta in his homeland. He threatened to leave the country if the democratic right and will to vote was ignored.

Paulo Di Canio: Fined for making what was perceived as a fascist salute while playing for Roman club Lazio. He once described himself as “a fascist, not a racist”.

Diego Maradona: The friendship between Fidel Castro, the Cuban leader, and the Argentinian player was constant and hugely beneficial to the latter. Castro gave Maradona access to Cuban healthcare when the former player was battling with addiction.

Oh, and Henry McLeish: East Fife alumni and second First Minister of Scotland.