Why the boundary changes won't devastate Labour
Labour will still win more seats than the Tories on an equal share of the vote.
David Cameron and Alex Salmond's duel over Scottish independence has overshadowed another issue of constitutional significance: the coalition's boundary changes. The publication of the Boundary Commission for Wales's proposals means we now have recommendations from all four UK commissions, allowing us to calculate the likely effect on each party.
It's often said that the boundary changes will lead to the longest period of Conservative government since Thatcher but the reality is more complex. The key point is that even after the boundary changes Labour will still win more seats than the Tories on an equivalent share of the vote. This is because the electoral bias towards Labour owes more to differential turnout (fewer people tend to vote in Labour constituencies) and regional factors (the Tory vote is poorly distributed) than it does to unequal constituencies (the coalition plans to fix constituency sizes at around 76,000 voters).
As a recent report by the University of Plymouth concluded:
The geography of each party's support base is much more important, so changes in the redistribution procedure are unlikely to have a substantial impact and remove the significant disadvantage currently suffered by the Conservative Party.
(Although the Tories, wedded as they are to first-past-the-post, can hardly complain.)
Thus, as YouGov's Anthony Wells shows, while the Tories need a lead of 7.4 per cent to win a majority under the new boundaries, Labour needs a lead of just 4.3 per cent. In addition, should the Tory lead fall below 2.2 per cent, Labour will emerge as the largest single party in a hung parliament.
There will now be a lengthy consultation on the boundary changes until October 2013 when the commission makes its final recommendations to parliament.
Below are the key figures in full.
To win a majority, Labour needs a lead of 4.3 per cent, compared to 3 per cent under the old boundaries.
Labour largest single party
To win the most seats in a hung parliament, Labour requires a Conservative lead below 2.2 per cent, compared to 4 per cent under the current system.
Conservatives largest single party
The Tories need a lead above 2.2 per cent, compared to 4 per cent under the old boundaries.
The Tories require a lead above 7.4 per cent, compared to 11 per cent under the current system.