Andy Burnham was left red-faced yesterday after he was fooled by an imposter posing as Donald Trump's chief of staff.

An international hunt is under way for the hoaxer who targeted the Prime Minister as he took office last month.

Mr Burnham thought he was swapping phone messages with Susie Wiles, the US President's no-nonsense 'enforcer', in the days before and after entering Downing Street.

But in an embarrassing debacle, which has left the PM 'looking like a chump', according to US officials, the British embassy in Washington was forced to flag to the White House that Mr Burnham had been duped.

No 10 refused to answer any questions yesterday amid concern at the ease with which security protocols were breached.

Security experts said the tactic could have been copied from Tehran's playbook, but Whitehall sources suggested it was orchestrated in the US.

Downing Street officials were asked why the Prime Minister was not more circumspect about the contact given that Ms Wiles' devices had previously been targeted by Iran. A spokesman would say only: 'We do not comment on national security matters.'

The official would not say how the exchanges unfolded or if Mr Burnham was embarrassed by them. 

Sources insisted that only a few messages of no significance were exchanged, no telephone conversation took place and the incident, first reported by Politico, was quickly flagged up to the authorities.

A source close to the White House said: 'Traditionally there would be a trusted chain of communications between British and US officials to make sure all communications were secure and formal.

'Of course, they're gonna say it's inconsequential, but it was clearly big enough that they alerted people to it.'

Professor Anthony Glees, a security and intelligence expert from the University of Buckingham, said: 'This looks like a bullseye as far as an attack is concerned.

'It is not an auspicious start to Burnham's relationship with Trump and his attempt to project himself on the world stage. To be duped like this is not a good look.'

Although prime ministers have previously been similarly fooled, Professor Glees said the hoax was a major security concern, adding: 'I think this is very serious. This is no laughing matter.

'For one thing, Burnham exchanged messages with someone he thought was Trump's chief of staff over several days, before and after he became Prime Minister.

'This is not two civil servants talking. This is a conversation as Burnham is taking the reins of power and you would expect Trump's chief of staff to discuss substantive issues. Susie's phone had been hacked before. You would expect someone in charge of Burnham's security to be aware of that.

'People in charge of his security, GCHQ and the FBI are the people with red faces here with a lot of explaining to do.'

Last May, Ms Wiles' phone was hacked by an impersonator who used her personal phone contacts to message other top American officials, seemingly using AI to replicate her voice in calls with prominent Republicans.

The key aide, who has been described by Mr Trump as the 'Ice Maiden', was also targeted by a cyber espionage unit associated with Iran's Revolutionary Guards in 2024. 

A hacker infiltrated her emails just before the 2024 election and threatened to disclose further emails to the media last June following the US bombing of Iran's nuclear sites.

Last night the White House said: 'This incident had nothing to do with the chief of staff's devices being hacked.'

The President, however, faced questions about Mr Burnham's judgment during an Oval Office press conference, during which he brushed it off as a 'miscommunication'.

It is understood that Ms Wiles changed her number and email after the hack last year and steps were made to secure her communications during an FBI investigation, which has yet to uncover the culprit.

Last night it emerged that personal mobile phone numbers for at least three Cabinet ministers, including the Defence Secretary, could be found online.

The numbers for Wes Streeting, Justice Secretary Alex Norris and Northern Ireland Secretary Chris Bryant were all available yesterday, but were taken down after it was flagged.

Former defence secretary Ben Wallace, who was duped into taking a hoax call in 2022, told Politico: 'This demonstrates our adversaries are always looking for weak points in our communications. If you are a government minister, always, always assume your mobile phone is compromised.'

Prerana Joshi, of the RUSI think-tank, warned: 'If your number is exposed, a whole host of malign, nefarious or even opportunistic cyber criminals or cyber actors could get hold of it.'

Andrew Bud, founder of iProov, which helps organisations protect against deep fakes, said: 'AI can easily copy faces and voices, meaning a familiar phone call or video is no longer proof of who is actually on the line, and anyone from the Prime Minister to a family member can be a target.'