The prospect of a Labour leadership challenge continues to mount as members of Jeremy Corbyn's shadow cabinet resign en masse.
But how would a potential leadership contest actually work?
A vote of no confidence has been tabled by Labour MPs for Monday's meeting of the parliamentary Labour Party. The secret ballot carries no formal weight but significant support for the motion would undoubtedly damage Corbyn's leadership and show a potential challenger if they were likely to have the requisite support from their colleagues to trigger a contest.
Any Labour MP wanting to challenge Corbyn would require the support of at least 20% of their parliamentary colleagues - at current levels, with 229 MPs, that equates to about 50 signatures.
Those MPs would have to signal their support for a challenger by writing to the party's general secretary.
Should the 20% figure be reached, a formal contest would then take place at the Labour Party's autumn conference at the end of September.
Any other MPs wanting to stand for the leadership would also need to reach the 20% figure in order to get on the ballot.
However, it is currently unclear whether Corbyn would automatically be on the ballot - but there is speculation that the Party's National Executive Committee could move to make that happen.
Once a line-up of candidates is finalised, the election would then take place on a one-member-one-vote basis with members, affiliates and registered supporters taking part.
If there were more than two candidates, voters would rank their choices and the winner would be the first to secure more than 50% of the vote. If nobody did so in the first round of counting, the last-placed candidate would have their votes reallocated and so on until a winner emerges.
However, when Corbyn was elected leader, he secured 59.5% of the vote in the first round after a surge in support from newly registered activists. He topped the ballot among party members, trade unionists and new supporters. That means any challenger would face an uphill battle to dethrone the current Labour leader - if he is on the ballot. Labour Party membership reportedly rose from about 200,000 in May 2015 to almost 400,000 in January of 2016 with much of that surge attributed to Corbyn.