Explainer - How does a leadership challenge to a Conservative prime minister work?

Prime Minister Theresa May's position as leader of the Conservative Party - and consequently her premiership - is under threat from lawmakers who are unhappy at the Brexit deal she has agreed with the European Union.The BBC reported on Tuesday, citing multiple sources, that a leadership challenge had been triggered, although there was no official confirmation of this.- WHAT NEEDS TO HAPPEN FOR THERE TO BE A LEADERSHIP CONTEST?