An economic agreement would, however be insufficient. A bold programme of constitutional reform would also be required, in order to attract the broadest coalition of voters. At its heart would be the introduction of some form of proportional representation for Westminster elections, so seats gained by each party match much more closely their national vote share. Electoral reform is a sine qua non of a progressive alliance – it ensures that such an alliance will only be needed once. After we have a proportional electoral system, centre left parties will be able to compete once again, without fear of splitting the anti-Conservative vote, and in the knowledge that they will be able to form a coalition once votes are counted. Of the parties that would make up a progressive alliance, only Labour does not currently support proportional representation, but it has supporters from all wings of the parliamentary party, from Jonathan Reynolds to John McDonnell, and, while not his priority, Jeremy Corbyn has expressed openness to top-up lists. While lukewarm, this tacit support for AMS/MMP, as used for the Scottish Parliament, the Welsh Assembly and the German Reichstag, is the most positive any Labour leader has ever been on proportional representation. So an agreement between centre-left parties on this crucial issue seems a genuine possibility.
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