The Cameroons believe they have come up with a policy that will deliver at least 20 more Tory seats at the next election. No. 10 is, understandably, determined to get this measure through: nothing else promises them anything like the same electoral dividend. But this silver bullet isn’t a tax cut or a new approach to Europe. It is a set of changes to the constituency boundaries.

This boundary review has been designed to limit the pro-Labour bias in the Westminster electoral system. It reduces the number of parliamentary seats from 650 to 600, which notionally reduces the number of Labour MPs by 28.

If its recommendations are enacted, the effect on British politics would be dramatic. The pollster Anthony Wells calculates that if an election were held today on the current boundaries, Labour would be two seats short of an overall majority. When you consider that there are five Sinn Fein members who don’t take their seats, that translates into a majority of sitting MPs. If, however, the election were held on the proposed new boundaries, the Tories would be two short of an overall majority. This would allow them to govern alone if they wanted.

Even under the new system, Labour would still have an advantage. The Tories would need, assuming a uniform national swing, to be seven points ahead of Labour to win an overall majority. At the last election, however, they needed a double-digit lead to achieve a majority.

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But the Prime Minister now faces a growing risk that the reform will fall victim to the tensions within the coalition. The last election convinced Cameron and his circle that, under the current system, it is almost impossible for the Conservatives to win outright. This explains why boundary changes featured prominently in the coalition agreement. In a straightforward quid pro quo, the two parties agreed that the government would hold a referendum on the alternative vote, which the Liberal Democrats wanted, and ask the boundary commission to conduct a review along lines that suited the Tories.

But the Liberal Democrats, still bruised by what they see as Cameron’s breach of faith during the AV referendum campaign, are now insisting that the boundaries and Lords reform are part of a package. Nick Clegg conceded to the Joint Committee on the Draft House of Lords Reform Bill on Monday that ‘there is no link between these elements’. Yet when I bumped into one of his senior advisers just two hours later, it was made clear that, in Clegg’s head, the link is very strong indeed. If Lords reform does not go through, the Lib Dems would not feel obliged to support the new Tory-friendly boundaries. Without Liberal Democrat votes, it would be difficult to get this electoral reform — which the Labour party detests, for obvious reasons — through the Commons.

Initially, the Cameroons’ attitude was to accept Lords reform. In private, the Prime Minister said that a small elected element in the Upper Chamber was not too high a price to pay. Others in Downing Street have been more direct. When I challenged a Cameron ally about the huge amount of parliamentary time any attempt to reform the Lords would take, the answer was ‘20 days of debate for 20 seats’.

But there is another risk: that the House of Lords itself may disrupt the government’s plans. The peers of the realm have realised that two can play the obstruction game. Age has not dimmed their instinct for self-preservation. They are muttering that if the coalition proceeds with Lords reform, the upper chamber will vote down the new boundaries for the Commons.

This is not an idle threat. The boundary changes have to pass through both houses. This is a rare example of the government having no power to overrule the upper house using the Parliament Act. If the Lords won’t back them, Cameron will have to fight the next election on the old Labour-friendly boundaries.

Those close to the Prime Minister fume that it would be ‘disgraceful for the Lords to interfere with boundaries for elections to the Commons’. But if the coalition really is prepared to use the Parliament Act to override objections to its plans for the second chamber, then it can hardly expect the Lords to respect constitutional convention in return.

Some Tories would not be too upset if the next election were fought using the existing constituencies. One Cabinet minister complains that ‘every time there’s a boundary review, we cock it up. The one after 1992 was meant to give us a boost and ended up giving Labour a whole load of seats.’ He accuses Tory HQ of being far too optimistic about how many seats they will gain under the new system. He points out that just under a third of the supposed Tory gains are meant to be in London, where population shifts are moving against the party so fast that any advantage probably will have disappeared by 2015. Moreover, these calculations are all based on past voter behaviour; they don’t take into account that a large number of left-wing Liberal Democrat voters have now moved to Labour.

There is also some grumbling on the back benches about the proposed changes. this is not surprising, since to create more winnable seats for the Tories you need to make their existing ones less safe. But the Tory high command remains convinced that it must pass the changes.  The result of the next election may well hang on whether they can.

This article first appeared in the print edition of The Spectator magazine, dated

Tags: Politics