FACTBOX: Rules governing Labour leadership elections

LONDON (Reuters) - Two former British cabinet ministers called on Wednesday for a secret ballot to decide if Prime Minister Gordon Brown should lead the Labour Party into an election due by June.

However, under Labour's constitution, the party's members of parliament cannot force a leadership election, and there is no proviso allowing for any such secret ballot.

Here are details of the Labour Party's rules for electing a leader.

THE RULES

The rules governing the election of a Labour leader are complicated and depend on whether there is a vacancy or not.

Under the rules, anyone wishing to challenge the leadership can only seek nomination before the party's annual conference.

Any nomination must be a member of the Parliamentary Labour Party (PLP) and requires the support of 20 percent of Labour MPs or it is declared null and void.

There can also only be a leadership election in these circumstances if the majority of Labour party members at the conference vote in favor of a challenge.

The candidate must then inform the party's general secretary and must win a further vote of party members allowing the challenge to go ahead.

THE VOTE

The voting is split equally three ways between Labour MPs and the Labour MEPs, party members and members of affiliated trade unions who have not opted out of paying a political levy.

The votes of each nominee in each section are then calculated as a percentage of the total votes cast in that section.

The ballot must take place at such a time which means the results can be declared at the annual party conference or at a special leadership election conference.

If any candidate receives a majority of votes, they are declared the leader. If not, the last place contender drops out and their second preferences reallocated, until someone passes the 50 percent figure.

(Reporting by Michael Holden; Editing by Elizabeth Fullerton)