The son of US President Donald Trump has blamed “elite” politicians for preventing Brexit taking place as promised on March 29.

Donald Trump Jr said that EU withdrawal negotiations, which could have been completed in months, had been allowed to stretch out for years because Prime Minister Theresa May failed to take his father’s advice.

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Donald Trump with his son Donald Trump Jr (Evan Vucci/AP)

And he said the British people need to “stand up for themselves against the global elite” to ensure that Brexit happens at the end of next week.

Mr Trump Jr’s comments, in an article for the Daily Telegraph, come just days after his father remarked that Mrs May had not listened to his advice on how to handle the Brexit process, which was now going “badly”.

The article is certain to spark speculation over whether Mr Trump Jr’s stance reflects the President’s thinking.

The younger Trump said that Mrs May should “honour” her oft-repeated promise to take the UK out of the EU on March 29.

And he raised the question of whether politicians’ assurances that they would deliver Brexit were in fact “a ruse”, quoting unnamed pro-Brexit politicians as suggesting that the Prime Minister may in fact be trying to “sabotage” the process.

“Since 2016, Prime Minister Theresa May has promised on more than 50 separate occasions that Britain would leave the EU on March 29 2019,” he said. “She needs to honour that promise.

“But Mrs May ignored advice from my father, and ultimately, a process that should have taken only a few short months has become a years-long stalemate, leaving the British people in limbo.”

Donald Trump Jr, who is executive vice-president of the Trump Organisation, drew parallels between delays in delivering Brexit and the investigations into his father’s alleged links with Russia.

“In a way, you could say that Brexit and my father’s election are one and the same,” he wrote.

“The people of both the UK and the US voted to uproot the establishment for the sake of individual freedom and independence, only to see the establishment try to silence their voices and overturn their mandates.

“What we’re seeing now in Washington, London and Brussels is the desperate, last-gasp attempt by those previously in power to cling on to what was once theirs in the face of an overwhelming mandate for change.”

He claimed that “the elites control London from Brussels” and that, as a result, “the will of the people is likely to be ignored”.

And he added: “With the deadline fast approaching, it appears that democracy in the UK is all but dead.”