Boris Johnson's leadership hangs in the balance as he waits for the release of Sue Gray's report into alleged rule-breaking parties in Downing Street.
A number of the prime minister's own MPs have already called on him to resign amid the allegations, but the PM has so far refused to step down.
For a Conservative party leadership contest to be triggered, a significant number of Tory MPs would have to turn against Mr Johnson.
MPs who want a leadership election signify that they have 'no confidence' in their current leader by writing a letter to Sir Graham Brady, chairman of the backbench 1922 Committee.
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