The Metropolitan Police has arrested a man on suspicion of selling a phone which belonged to Morgan McSweeney at a time when he was the prime minister's chief of staff.
In a statement, the police said officers investigating the theft of a mobile phone in Pimlico, London, in October 2025 had arrested "a 28-year-old man on suspicion of handling stolen goods".
"The arrest took place on Wednesday, 29 April at an address in Peckham.
"The man was taken into police custody and later bailed. He is suspected of receiving the phone after it was stolen and then selling it on. He is not suspected of any involvement in the original theft. The phone has not been recovered."
The theft of McSweeney's government phone came to light earlier this year, as the government was publishing documents about the appointment of Lord Mandelson as the UK's ambassador to the US.
McSweeney was an ally of Lord Mandelson and advised the prime minister to select him for the diplomatic role – something which he has since said was a mistake in light of the peer's longstanding relationship with the convicted sex offender Jeffery Epstein.
It is thought his phone could contain messages that provide further information on the process that led to the appointment.
The phone was stolen in October, one month after Lord Mandelson was sacked, but several months before MPs voted to compel the government to publish the relevant messages.
McSweeney reported the theft at the time but due to an error the location was incorrectly recorded as having happened in Belgrave Street in Tower Hamlets, east London, rather than in Belgrave Road in Westminster.
The police said that McSweeney had not disclosed to the police a the time that he held a senior government role or the security implications of having his phone stolen.
In March, the police - facing criticism that it had not properly investigated the theft - took the unusual step of publishing the transcript of McSweeney's 999 call.
Following the discovery that officers had recorded the wrong address, the police said they were reassessing the evidence.
Speaking to a parliamentary committee last month, McSweeney said he had told Downing Street about the theft immediately after it happened and had hoped they might be able to track the phone.
Asked if his phone contained messages relating to Lord Mandelson's appointment, McSweeney said: "Probably not much about his appointment that hasn't already been available to No. 10."
He said that when Lord Mandelson was sacked, Downing Street had conducted research into the appointment and he had been asked to "share messages and emails about the appointment".
"Everything that I had at that time in September, which was more than a month before my phone was stolen, I shared it with the No 10 team."
