With everyone and his Labour dog calling for tactical voting, the always-good-value Tim Harford made an important point on the Today programme this morning. He says that about 10 per cent of voters report having voted tactically in previous elections. That might not sound like much but in most constituencies it is usually more than enough to determine the difference between coming first and coming third.

The important point, though, was the one he made next: that if you are considering voting tactically, it is important to check the facts about the position in your constituency. Leaflets shoved through the door make all sorts of claims, and so do canvassers on the doorstep, but it crucial to check the facts for yourself, because constituency boundaries have changed all over the country. This means that simply looking up the results for 2005 aren’t enough, you need to check what the results would be if the constituencies had been tweaked to reflect their current boundaries. (It is because of this that there are oddities such as lists which show seats that are currently Tory as Tory target seats – i.e., seats they’re trying to win from Labour. The point in these cases is that post-tweaking, the relevant constituencies would be Labour seats on past voting patterns. So even though the seats are currently Tory, in this election they would count as wins from Labour, because if the boundary changes had been in effect in 2005 they would have been Labour at the last election. I’m glad that’s clear.)

What we badly need is a non-partisan website which takes the 2005 voting and plugs in the 2010 boundaries to tell you what the voting pattern would have been with current boundaries. That is very important information for anyone planning to vote tactically. If only that site existed... but wait! The BBC have done exactly that at their election website. In fact they go a step further and give the 2005-tweaked to-2010 data as their default setting when you look up your Parliamentary constituency. Any tactical voters out there, don’t neglect to check.