Theresa May’s decision to invite Donald Trump to a state visit has put the Queen in a “very difficult position”, a former head of the Foreign Office says.
In a letter to The Times, Lord Ricketts said the offer had been “premature”.
A petition calling for the state visit to be cancelled has already gathered more than 1.5 million signatures.
On Monday, thousands of people across the UK joined protests against Mr Trump’s travel ban on seven mainly Muslim countries.
The controversial immigration measures prompted an emergency debate in parliament on Monday.
Lord Ricketts, who was permanent secretary at the Foreign Office from 2006-10, said it was unprecedented for a US president to be invited for a state visit in their first year in the White House.
He questioned whether Mr Trump was “specially deserving of this exceptional honour”.
“It would have been far wiser to wait to see what sort of president he would turn out to be before advising the Queen to invite him. Now the Queen is put in a very difficult position,” he said.