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Mr Borrell, a former President of the European Parliament, said President Trump insisted the type of border wall with Mexico he has vowed to make his southern neighbours pay for would work for Europe as well.

The respected Spanish politician did not reveal when the controversial US leader put forward his radical solution, although diplomatic sources suggested it had been in June when he flew to the States in a trip coinciding with the visit to the White House of the Spanish King and Queen.

Mr Borrell revealed President Trump’s Saharan wall “solution” during a lunch in Madrid organised by cultural association Club Siglo XXI, which was formed in 1969 and is known for holding respected debates, conferences and forums.

Spanish daily El Pais said that he had made it clear he disagreed with Donald Trump’s diagnosis but insisted a policy had to be put in place to deal with the fact Africa would double its population in the next 20 years.