Mr Cruz expressed outrage over reports the Government initially decided to not allow American jets to deploy from British bases to launch strikes on Iran. The US President said he was “not happy” with the UK over the decision as it led to American aircraft “flying many extra hours” over the weekend. Mr Trump said Sir Keir is “no Winston Churchill” and Mr Cruz has also criticised the PM.

Speaking to The i Paper, Mr Cruz said: “The British Prime Minister’s decision to disregard that long-standing friendship and alliance is disturbing and dangerous and does real damage to the special relationship.

He added: “A Prime Minister whose political prospects are plummeting at home seeking out conflict with the United States is not in the interest of America or in the interest of the United Kingdom.”

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He said the proposal is “deeply harmful to US national security, and not in the interest of the British people”.

Mr Trump told The Sun the US-UK alliance is “obviously not what it was”, claiming Sir Keir “has not been helpful” in the Middle East conflict.

Downing Street has played down the rift, insisting the UK and US remain “staunch” allies. Sir Keir on Sunday granted the US permission to use British airbases to launch “defensive” strikes on Iranian missile sites, a day after the US and Israel first launched military action against Iran.

The Prime Minister told his Cabinet on Tuesday this was “lawful and in the national interest”. It is believed the UK was previously concerned that allowing the US to use its bases to conduct strikes on Iran could breach international law.

The Government has published a summary of its legal position, setting out that the UK was acting in defence of itself and “collective self-defence of regional allies who have requested support”.

Sir Keir has insisted the UK is not participating in any “offensive action”, but UK military planes and personnel continue to provide defensive support to allies in the region amid continued Iranian retaliation attacks.

Critics of the PM have accused him of looking “weak” for his stance over the conflict.