A committee of lawmakers has requested diaries, emails, photos and mobile phone messages from Boris Johnson's office as part of an inquiry into whether the prime minister misled parliament over Covid-19 lockdown-breaking events in Downing Street.
The Privileges Committee will look into whether Johnson, who last week said he would step down following growing pressure to do so from many of his own ministers and lawmakers, misled parliament with his various comments on so-called partygate.
The committee's investigation was triggered by a vote in parliament.
Convention dictates ministers who are found to have knowingly misled parliament should offer their resignation. As Johnson has already said he will step down, such a verdict would only affect perception of his time in office.
Johnson initially told parliament that his Downing Street office had followed all lockdown rules during the Covid pandemic, only for an internal report to find it had held several alcohol-fuelled parties at that time.
The prime minister was also fined by police over a gathering for his 56th birthday. He denies deliberately misleading parliament, and says he did not realise he was breaking the rules. He has apologised for his conduct.
The committee said it had written to Johnson and Cabinet Secretary Simon Case to request a wide range of documents including the prime minister's diaries for dates on which gatherings took place in his Downing Street residence and office.
Emails, Whatsapp messages, entry logs for 10 Downing Street, legal advice received by Johnson or commissioned by his office, and briefing packs prepared for the prime minister ahead of his appearances in parliament were also among the documents requested by the committee.
It has also asked for details of any relevant documents known to have existed which were subsequently deleted.
The committee said it expected to begin oral evidence sessions after parliament returns from its summer break in September.