Nick Clegg is set to announce the date of the AV referendum to the House of Commons today. As I reported on Friday, it is expected to be on May 5th, the same day as the local elections and the Scottish and Welsh elections. Downing Street has now said that, despite some rumours to the contrary, Cameron will be backing first past the post, though whether this will take the form of actively campaigning for a No isn't clear.

The 1922 backbench committee, meanwhile, is making plans to disrupt the referendum. Bernard Jenkin told the Guardian that if ministers did not give ground on changing the date, he would be prepared to table amendments. He also said that he would demand "a high threshold" for the Yes "possibly modelled on the system used for the Scottish devolution referendum in 1979." A majority of voters (51%) wanted a Scottish parliament in 1979 but the referendum was annulled because it failed to win the support of 40% of the electorate as required by an amendment to the Scotland Act successfully championed by opponents of devolution within Labour.

This is, quite unashamedly, an attempt to wreck reform and frustrate democracy. It would be absurd if such a threshold were introduced. If Jenkin had been calling for a 40% threshold for every referendum we've had in this country as well as for elections then you could at least say he was being consistent. But of course he hasn't.

If the 40% rule were to be applied to elections to the House of Commons then only 35 MPs out of 650 would have been elected at the last election (see this chart by James Graham for a full breakdown). Jenkin himself, who only received the support of 32.5% of the electorate in Harwich and Essex North, would not have been elected.

By way of response, opponents of AV might object that voting reform is a fundamental constitutional issue, different from electing MPs, and therefore different principles should apply. But that argument is nonsense, especially in a country that does not have a written constitution which sets out how these things ought to be done and hasn't endorsed first past the post.

Once elected, the British government can do pretty much as it wants, including making huge constitutional changes. But you don't hear Jenkin calling for all governments to have the support of at least 40% of the electorate. Indeed, given his trenchant support for first past the post - which returned a government in 2005 with only 22% support - we can take it he wants the exact opposite to apply.

So we should see Jenkin's scheme for what it is: a blatant attempt to frustrate the democratic will of the people in the event of them backing AV. It would be a disgrace if this were to get any further than his whingings to the press.