Sir Ed Davey is pressing the Prime Minister to advise King Charles against travelling to Washington for a State Visit scheduled for late April.
The Liberal Democrat leader maintains that proceeding with the trip would deliver a significant victory to President Trump while American and Israeli forces conduct military operations against Iran.
The King and Queen Camilla are anticipated to meet Donald Trump ahead of celebrations marking 250 years since American independence next July, though Buckingham Palace has yet to formally announce the engagement.
Sir Ed argues the current geopolitical climate makes such a high-profile royal engagement inappropriate given escalating Middle East tensions.
Sir Ed Davey is pressing the Prime Minister to advise King Charles against travelling to Washington for a State Visit scheduled for late April.
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Transatlantic relations have deteriorated sharply since Sir Keir initially declined to permit American aircraft to use British military installations for offensive bombing raids on Iran.
The government subsequently reversed course, granting permission for US forces to conduct "defensive" strikes targeting Iranian missile launch sites.
RAF aircraft have additionally been deployed to shoot down Iranian drones and missiles.
These decisions drew pointed criticism from the American president, who last week declared Sir Keir was "no Winston Churchill" and accused him on Saturday of seeking to "join wars after we've already won".
Sir Keir attempted to downplay the diplomatic friction on Monday, emphasising that security personnel from both nations continue to collaborate daily "as they always have".
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The two leaders held their first telephone conversation since tensions escalated on Sunday, with Downing Street providing minimal information about the exchange.
Sir Keir attempted to downplay the diplomatic friction on Monday, emphasising that security personnel from both nations continue to collaborate daily "as they always have".
The Prime Minister maintained his defence of Britain's approach to the Iran conflict, stating he was acting in line with "our principles" and "Britain's best interests".
His comments suggest Number 10 is seeking to move past the public disagreement with Washington, despite Trump's barbed remarks about British leadership.
The limited disclosure from Downing Street regarding Sunday's call between the leaders indicates a cautious approach to managing the transatlantic relationship during this sensitive period.
Sir Ed Davey has urged the Prime Minister to advise the monarch that the trip to America should be called off.
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In his statement, Sir Ed urged the Prime Minister to advise the monarch that the trip "should be called off", adding: "At a time when Trump has launched an illegal war that is devastating the Middle East and pushing up energy bills for British families, it's clear this visit should not go ahead."
He argued that granting such an honour to "someone who repeatedly insults and damages our country" would represent "yet another huge diplomatic coup for President Trump".
Within Labour's ranks, one MP predicted Sir Keir would "almost certainly" face mounting internal pressure to scrap the royal visit as April approaches.
Those battling Green Party challenges in May's English local elections are particularly anxious about appearing insufficiently robust towards the American president.