Conservative MPs have triggered a vote of no confidence in Theresa May, plunging the Brexit process into chaos as Tory colleagues indicated they no longer had faith in the prime minister to deliver the deal.
Sir Graham Brady, the chair of the 1922 Committee, has received at least 48 letters from Conservative MPs calling for a vote of no confidence in May. Under party rules, a contest is triggered if 15% of Conservative MPs write to the chair of the committee of Tory backbenchers.
A ballot will be held on Wednesday evening, Brady said.
Forty-eight Conservative MPs would need to back a no-confidence vote in Theresa May to trigger a leadership contest, according to party rules.
There are two ways a contest can be triggered, most obviously if the leader of the party resigns. If they do not, 15 percent of Conservative MPs must write to the chairman of the 1922 Committee of backbench Tories. With the party's current crop of 317 MPs, 48 would be needed.
After David Cameron announced his resignation , five Tory MPs stood for the leadership. Unlike Labour party rules, under which candidates go to a ballot of members as long as they have the support of 15 percent of the party's MPs, Conservative candidates are whittled down to a final two before party members have their say.
The ballot is based on "one member, one vote", but in 2016 one of the final two candidates, Andrea Leadsom, withdrew from the race after a damaging interview with the Times about the fact that May did not have children. Her withdrawal meant May was made party leader without having been elected by members.
The prime minister will now need the backing of at least 158 Tory MPs to see off the Brexiters' challenge, and her position would then be safe for 12 months. However, the prime minister could decide to resign if votes against her were below the threshold to topple her, but significant enough in number.
More than 20 other Tory backbenchers have publicly confirmed they have submitted letters calling for May to step down over her Brexit proposal, including Jacob Rees-Mogg, the influential chair of the European Research Group, the former Brexit minister Steve Baker and fellow leavers Nadine Dorries and Andrew Bridgen.
Brexiter MPs had hoped to oust the prime minister some weeks earlier after she presented her withdrawal agreement but progress then appeared to stall ahead of the meaningful vote. It was her decision to cancel that vote, in the face of huge defeat, that appeared to lead to a slew of new letters - though not all writers have gone public with theirs.
Not all the letters have been sparked by the draft withdrawal agreement or the delay to the vote. Several were prompted months earlier by the Chequers agreement, which saw the departure of two cabinet ministers, and the disastrous Salzburg summit where that was rejected.
James Duddridge announced he had submitted his letter during the Conservative party conference. Another MP Simon Clarke withdrew his letter before the summer but then resubmitted it.
Others who have submitted letters include the ERG deputy chair, Mark Francois, backbenchers Henry Smith, Andrea Jenkyns, Philip Davies, Sheryll Murray, Anne Marie Morris and the former culture secretary John Whittingdale.