How the Labour leadership result changes under a one-member-one-vote system

Had MPs' votes been treated in the same way as party members', Ed Miliband would have won a landslide victory.

One of the likely consequences of Ed Miliband’s decision to introduce a new opt-in system for donations to Labour from affiliated trade union members will be a major change to the party’s leadership election system. At present the decision lies with an electoral college split three ways between the party’s 272 MPs and MEPs, all party members (193,000 at the last count) and members of affiliated trade unions and socialist societies (around 2.7 million).

But should Miliband make all trade unionists who choose to donate full members of the party (as his speech on Tuesday implied), the third of these sections would effectively cease to exist (most socialist societies already require their members to be members of Labour). This would inevitably raise the question of whether the party should introduce a pure one-member-one-vote (OMOV) system, with MPs’ votes no longer given greater weight than those of party members. As I noted in 2010, Labour is the only one of the three main parties which does not give the final say to individual party members. Under the electoral college system, the vote of one MP is worth the votes of 608 party members and 12,915 affiliated members and the vote of one party member is worth the votes of 21 affiliated members.

But would a one-member-one-vote system have changed the outcome in 2010? Earlier today, I reran the election using a OMOV model to discover the answer. It’s not a perfect simulation; I don’t have the data needed to strip out multiple votes (most MPs, for instance, had at least three votes by virtue of their membership of affiliated societies) and it’s hard to know how many trade unionists would have participated under an opt-in system, but it’s the best guide currently available.

While the result does not change significantly (all the candidates finish in the same position, except Diane Abbott, who leapfrogs Andy Burnham and Ed Balls in the first round), it is notable that Ed Miliband’s margin of victory increases dramatically from just 1.3 per cent to 8.8 per cent. Since David Miliband won the MPs’ section by 140 votes to 122, his share is heavily reduced under a OMOV vote. He also won the party members’ section by 66,814 to 55,992, but Ed’s huge lead among affiliated members (119,405 to 80,266) means he pulls ahead.

Given how often it’s claimed that he wouldn’t have won without the support of the “union barons” (the “block vote” was abolished by John Smith in 1993), Miliband’s speech was, among other things, a subtle reminder that it was thousands of individual votes that delivered him victory.