Simon Hix and Nick Vivyan at LSE provide the most useful UK poll tracking and election prognoses that I’ve seen.
The dots in the figure show the results from the various polls and the shaded areas around the lines are the 95 per cent confidence intervals around the mean standings of the parties. … As of 26 April, the national standing of the parties was 33.3 per cent for the Conservatives (up 1.0 per cent from our 19 April analysis), 26.5 per cent for Labour (down 0.3 per cent), and 29.3 per cent for the Lib Dems (down 0.8 per cent).
It’s pretty clear from this that the first television debate did have substantial – and lasting – consequences for Lib Dem support. And remember – the UK has a relatively short campaign season, so that unless voters change their minds soon, this will plausibly have consequences on election day. Hix and Vivyan also examine how these numbers are likely to translate into seats under a variety of assumptions. Despite significant differences in number of seats, the basic picture remains stable across various assumptions. The Conservatives will have the largest number of seats – but not a majority. Smaller parties (regional parties) will not have enough seats to support a Conservative majority government on their own, let alone a Labour majority. The Liberal Democrats will have enough seats to either ally with the Labour party or the Conservatives so as to create a majority in the House of Commons and thus form a government. Obviously, projections can go wrong; a week is a long time in politics etc. But given current information, it is hard to imagine the Liberal Democrats being in a better strategic situation to choose a coalition partner, and to demand major electoral reform as part of their price.