Andy Burnham yesterday became the first of the Labour leadership candidates to criticise the party's voting system and the disproportionate power that MPs wield under it.

As I've pointed out before, the party's tripartite electoral college (divided between MPs/MEPs, party members, and affiliated trade unions and socialist societies) means that some votes are worth significantly more than others. The vote of one MP is worth the votes of 608 party members and 12,915 affiliated members. The vote of one party member is worth the votes of 21 affiliated members.

The system, which dates from 1993, is an improvement on what came before. In the pre-1981 era, leaders were elected by the Parliamentary Labour Party alone and until 1993, affiliated societies controlled 40 per cent, rather than 33 per cent, of the vote. But the electoral college system puts Labour out of step with the Tories and the Lib Dems, which elect leaders using a one-member-one-vote system.

It would be a mistake for Labour to adopt this system in its purest form. It is both just and necessary for affiliated trade unions, as the founders of the party, to have a say over the leadership. But the extraordinary power held by the PLP can no longer be justified.

As a Guardian editorial warns today, a leader could one day be elected without the majority support of ordinary party members. Labour's new leader should act to ensure their successor does not suffer this fate.