"Yesterday, the Conservative Party suffered its worst single electoral setback since Black Wednesday". Discuss.

By Tim Montgomerie
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On last night's World Tonight I claimed that the loss of boundary reviews was the single worst political event to hit the Tories since 1992 and Black Wednesday*. Was I exaggerating?

When the Parliamentary and Voting Constituencies Bill was passed I celebrated the moment, noting that the introduction of fair-sized seats of equal population could boost the number of Tory MPs at the next election by up to twenty. That was certainly Conservative HQ's view. This morning the hope of boundaries fairness** is close to death, if not dead. After having explicitly said there that there was no connection between Lords reform and equal-sized seats Nick Clegg has u-turned and claimed there needs to be a connection.

It's hard to think of another single policy or political choice that can win twenty Tory seats - not just at one general election but for the foreseeable future. Without the boundary review we have to win about 3% more at the next election because the Conservative Party needs a 10.5% lead to win an outright majority on existing boundaries but a more modest 7.6% on what were to be the new boundaries. 3% is not a small amount. It's not much less than we gained from the whole 2005 to 2010 effort.

The only advantage of the likely defeat of boundary changes is that a central plank of the Cameron/Osborne battleplan has gone. Any residual complacency must have gone. They can't carry on as they were. They need a game changer and, preferably, soon.

** I opposed ERM membership and although Black Wednesday was good for the economy it had a huge impact on the Tory reputation for economic competence.

** Boundaries "unfairness" is one of the explanations for why Labour get a majority with a 3% lead in the popular vote while Conservatives need an 11% lead for the same result. Or to put it another way John Major got a majority of 21 in 1992 with an 8% lead and a 42% share of the vote while, in 2005, Tony Blair got a 66 majority with just 36% of the vote and a 3% lead.