Labour MPs are said to be seeking support for a leadership challenge to Prime Minister Gordon Brown. But what are the Labour Party's leadership rules?
To challenge an incumbent leader in power:
Under Labour Party rules a challenge to a sitting prime minister requires 20% of Labour MPs to nominate an alternative candidate. That nominee must accept the nomination and then inform the general secretary of the Labour Party, in writing, of his or her intention to stand. Following this, at a session of annual conference there must be a card vote allowing such a challenge to go ahead. At the moment there are 350 Labour MPs (not including the Speaker) - therefore 70 signatures would be required by any nominee for an effective challenge. The reference to a "session of annual conference' in the rule book does not mean that it has to happen at the scheduled annual party conference - the party can convene special sessions of annual conference.
If Gordon Brown decided to quit:
If Gordon Brown stepped down a short-term replacement would be chosen by the cabinet in consultation with the Labour Party National Executive Committee. The caretaker job does not necessarily go to the deputy Labour leader - currently Harriet Harman. The Labour Party NEC will then set out a timetable for electing a successor; there are very few constraints upon this except that time must be provided for affiliated organisations to ballot their members. Those wanting to stand would require nominations from 12.5% of Labour MPs - currently 44 MPs.
Once there is a contest, who votes?
Labour's electoral college is divided into three sections. Each section makes up a third of the result. The sections are:
1) Labour MPs and Labour MEPs
2) Labour Party Members
3) Affiliated organisations (trades unions and socialist societies). They must ballot their members and divide their votes proportionately.