The former Liberal Democrat leader joined a growing number of British politicians in blasting the president’s policy.
He accused the Republican and other “extreme right-wing” party leaders of stirring up “division, conflict and tyranny”.
The ban, which came into affect on Saturday, sees citizens from Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen temporarily barred from entering the US for 90 days.
Lord Paddy Ashdown said he was "frightened to death" by Donald Trump
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Donald Trump represents something that frightens me to death
Lord Paddy Ashdown
President Trump said the restrictions, a key pledge of his during the election campaign, was necessary for “searching out terrorists” in his conquest to defeat Isis.
But, speaking on Sky News on Monday, Lord Ashdown said he was left terrified by the executive order.
“Donald Trump represents something that frightens me to death,” he said.
The former Liberal Democrat leader said the US President put liberal values at risk
“You have never seen a Government that has been successful, an economy that has been prosperous or an age that has been peaceful that has not been based on broadly liberal values that we respect each other.
“Donald Trump along with many, many others who are appearing on the extreme right-wing in the Western world are not attached to that principle.”
The 75-year-old peer warned Western values were under threat with Donald Trump as leader of the free world.
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President Trump signed the travel ban executive order on Saturday
“If you abandoned that principle like he clearly has done in this case, then what inevitably follows – and history is very clear – is division, conflict and tyranny,” he continued.
“I think that great liberal value that upon which our society is based is now more seriously at threat than ever before with Donald Trump in the van.”
Earlier on Monday, Lord Ashdown took to social media to call on President Trump’s proposed state visit to the UK to be cancelled.
He wrote: “Am I alone in finding it impossible to bear that in pursuit of her deeply wrong-headed policies our PM is now forcing THAT MAN on our Queen?"
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Trump speaks briefly to reporters as he arrives aboard Air Force One at Joint Base Andrews
A petition to stop it has gathered over 1.3 million signatures since the ban was introduced over the weekend – sparking emergency protests to take place across the UK on Monday.
Despite the backlash, Downing Street remained adamant the visit will still go ahead.
A spokesman said: ”The USA is one of this country's closest allies, and we look forward to hosting the president later this year."
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