Police are revisiting a closed investigation into the theft of Morgan McSweeney’s phone after admitting they recorded the wrong address when he reported the crime.

Keir Starmer’s former chief of staff told the Metropolitan police that his phone was stolen in central London when he was returning home from a restaurant on 20 October last year, the Times reported.

The phone is thought to hold messages relating to Peter Mandelson’s appointment as British ambassador, which could be lost if the phone remains unfound. Earlier on Tuesday, the Met had said they were “too busy” to investigate the snatched phone.

The WhatsApp messages of aides and ministers are due to be published in the next tranche of the Mandelson files and the prime minister is said to be braced for potential further resignations over their contents. McSweeney resigned in February over his role in Mandelson’s appointment as ambassador to the US.

All senior ministers, civil servants and special advisers have been asked to have their phone messages examined, including those no longer in government such as McSweeney and the former communications director Matthew Doyle, as well as the former deputy prime minister Angela Rayner. But the theft of McSweeney’s work phone means his WhatsApp messages and texts to Mandelson cannot be examined.

Thousands of documents in the second tranche of the Mandelson files – expected to include informal communications alongside formal messages like those in the first batch – are expected to be released after Easter.

The releases were forced by a parliamentary motion passed by the Conservatives after Mandelson was sacked in September, nine months into his role as US ambassador, after new details emerged about his ties to Jeffrey Epstein.

The former Labour peer was arrested in February on suspicion of misconduct in public office after emails from the US Department of Justice’s Epstein files appeared to show he forwarded confidential information to Epstein while he was business secretary in Gordon Brown’s government.

Mandelson has since been released from bail conditions while he remains under investigation, and denies any wrongdoing. His lawyers have said he does not intend to make any further statement at this time.

The State of It, the Times’ political podcast, reported that McSweeney told police the phone was taken by a man wearing a balaclava on an electric bike. During the theft, first reported by the Sun on Sunday, the man is said to have grabbed the device out of McSweeney’s hand as he was responding to text messages before cycling away. McSweeney gave chase but was unable to keep up.

Initially, the Met said officers were “too busy” to speak to McSweeney directly. He was given a crime reference number and the case was closed.

But on Tuesday evening, the force said that while responding to a recent media inquiry, it became aware that an incorrect address was recorded at the time of the initial call to police and it should have been noted as Belgrave Road in Westminster.

Police said the error will now be amended and the force will reassess whether there is available evidence.

McSweeney reported the theft of his phone to No 10, the device was shut off remotely and he was given a new one with the same number the next day.

A Met spokesperson said: “On Monday 20 October police received a report from a man in his 40s alleging that his phone had been snatched.

“The incident was recorded as having taken place in Belgrave Street, E1.

“A review of the allegation, including a consideration of whether there was available CCTV, did not identify any realistic lines of inquiry. The investigation was subsequently closed.

“In the course of responding to a recent media inquiry, we became aware that the address was entered incorrectly at the time of the initial call and should instead have been recorded as Belgrave Road, Pimlico.

“Having identified this error, the report will be amended and the assessment of whether there is available evidence revisited.”