A breakthrough may have been made in attempts to unlock Boris Johnson’s old mobile phone.

An ally of the former prime minister has suggested that a “version” of the device’s PIN has been found by the government.

The phone was used until May 2021, and likely contains WhatsApp messages related to the ordering of coronavirus lockdowns – as well as the Johnson administration’s early response to the pandemic.

On Monday, the government missed a deadline to hand over this evidence to the COVID inquiry.

According to The Times, the delay was because Mr Johnson had forgotten the password to the phone.

Mr Johnson’s spokesperson did not deny the claims to Sky News – instead saying that government-appointed “technical experts” were continuing to work “to recover material safely from the device”.

Yesterday, one of his allies said: “It is not true that Boris does not remember his PIN number, it is just that he does not have 100% confidence he remembers it.

“Separately, the government has found its own version of the PIN.”

He was advised not to access the phone again on security grounds while serving as prime minister after it emerged his number had been freely available online for 15 years.

Whitehall officials were known to be trying to securely retrieve the messages on the phone, which is being held by Mr Johnson’s lawyers.

The Cabinet Office has been contacted for comment about the suggestion technicians have discovered a past code that Mr Johnson used.

According to The Times, there are concerns the contents could be wiped if the wrong combination of numbers is entered.

The newspaper has also reported that the device was last accessed in December 2021 after Lord Geidt – then the prime minister’s adviser on ministerial interests – asked for WhatsApp messages relating to an investigation about the funding of the refurbishment of the Downing Street flat.

If accurate, this would suggest that the phone has been opened since Mr Johnson was told to no longer use it.

Mr Johnson’s spokesman has been approached about the claim.

The Cabinet Office had until 4pm on Monday to hand over the unredacted WhatsApp messages from Mr Johnson’s previous phone after it lost a legal challenge.

Click to subscribe to the Sky News Daily wherever you get your podcasts

Ministers had fought a request from inquiry chairwoman Baroness Heather Hallett to release his uncensored messages, notebooks and diaries from his time in Downing Street, arguing they should not have to hand over material that was “unambiguously irrelevant”.

But the argument was dismissed by the High Court last week.

The government has since handed over the rest of Mr Johnson’s documents, except for the messages from the locked phone.

The inquiry, which heard evidence from Levelling Up Secretary Michael Gove yesterday, is understood to be aware of the efforts to securely extract any potentially relevant content from Mr Johnson’s old phone.

A mobile security expert has cast doubt on claims the messages cannot be accessed because of a memory lapse on Mr Johnson’s part.

Andrew Whaley, senior technical director at Norwegian cybersecurity company Promon, said: “This is a pretty lame excuse. Provided Boris’s WhatsApp is backed up, accessing the data would take minutes.

“As this is a diplomatic phone, the security measures may very well be different, but even still, it’s not an impossible task by any means.”

The COVID-19 Bereaved Families for Justice group said it was a “complete joke” and Mr Johnson “needs to take full responsibility” for handing over his WhatsApp messages.