Germany is greatly understating the true size of its current account surplus in order to deflect mounting global criticism, according to an exposé by German economists.

The annual surplus in ‘real’ terms – the figure that matters in trade relations – may be as much as €80bn (£70bn) higher than the sum declared by the statistics office and submitted to international bodies.

“They’re cooking the books so that the surplus does not look as if it is increasing. What they are doing is a form of ‘political smoothing’, but very few people understand this,” said Professor Heiner Flassbeck, Germany’s former state-secretary of finance and now at Hamburg university.

The allegation comes at a sensitive moment, just as US President Donald Trump gears up for a showdown with Europe over trade. "I've had a lot of problems with the European Union, and it may morph into something very big from a trade standpoint," he told broadcaster Piers Morgan.

"It's a very unfair situation. We cannot get our product in. It's very, very tough, and yet they send their product to us – no taxes, very little taxes."