Donald Trump was labelled a "serial child abuser" as MPs urged Boris Johnson to condemn the US President's migrant separation policy which has seen children held "in cages".
The Foreign Secretary was also urged to cancel Mr Trump's planned visit to the UK next month after international uproar over his "zero-tolerance" policy to illegal immigrants.
The policy, introduced in May, has seen more than 2,300 migrant children placed in detention centres -- as they cannot legally be jailed alongside their parents.
SNP MP Peter Grant, speaking during Foreign Office questions in the Commons, described the facilities as "concentration camps".
He said: "Isn't it time for the Government to seriously question whether the United States' present President is a fit and proper person to be our greatest ally?
'Putting children into concentration camps is not acceptable'
"This is somebody who can only be described as a serial child abuser.
"Putting children into concentration camps is not acceptable. He has not yet taken them out of these camps, he's holding them hostage to force their parents to give up their claims to asylum.
"He's also tried to abolish due process. How can this person be fit for a state visit?"
Mr Johnson responded that the president had since repealed the policy, adding: "He remains the head of state of our most important economic, military and security ally."
'Why he thinks seriously that a man like that should have the honour'
Shadow foreign secretary Emily Thornberry later said: "Even he knows, in the depth of his soul, that when we have a president like Donald Trump who bans Muslims and supports Nazis, who stokes conflict and fuels climate change, who abuses women and cages children, that is not a record to be admired, that is a record to be abhorred.
"I simply ask the Foreign Secretary, not just why he joked that a man like that should be in charge of our Brexit negotiations, but why he thinks seriously that a man like that should have the honour, in two weeks' time, of visiting Chequers, Blenheim Palace and Windsor Castle and shaking hands with Her Majesty the Queen?"
Mr Johnson responded: "We're not afraid to say it when our views differ, but the fundamental point on which I think she and I are in complete agreement is that it is right that the United Kingdom should welcome to this country the head of state of our most important and most trusted ally.
"She is on record as saying that in the past; if she now dissents from that view that would be surprising and I'd be interested to hear it from her own lips."
Ms Thornberry was unable to respond as she had exceeded her two-question limit for Foreign Office questions.