The question is not whether the Lib Dems will lose, but how badly they will perform

One big question hangs over Thursday's local council elections that take place in most of England outside London: just how badly will the Liberal Democrats do?

The party has long been master of the art of fighting local elections. It regularly manages to persuade voters to lend it their support locally even though they refuse to back the party in a general election.

Estimates of the Liberal Democrats' "projected national share" at each year's annual round of local elections are often some five points or so above their current standing in the national polls.

But the party's national standing is now dire. Its current rating in The Independent's latest poll of polls is only 11 points, nine points down on four years ago, when the seats being fought over this Thursday were last contested.

Defending more than 1,800 seats, the party seems bound to suffer serious losses unless it can persuade many more people to forget their doubts about the national party and give it their local vote. A greater willingness by third-placed Tory voters to make a tactical switch to the party might help.

But the party's fear must be that discontent with its role in the Coalition means that many of those who hitherto have backed the party locally will now no longer be willing to do so.

Some of the party's most prized possessions are at stake: control of Bristol, Hull and Newcastle could all be lost if the tide matches that in the national polls. Overall, the party could lose control of half the 22 councils it is defending.

Such an outcome might well prove a greater source of discontent within the party than defeat for the Yes side in the AV referendum.

If the Liberal Democrats face next week's elections with trepidation, Labour activists are hopeful. Four years ago the party was down at 30 per cent in the national polls, as Tony Blair eked out the final weeks of his premiership. But Labour's support stands now at 39 per cent.

The results on Thursday present Ed Miliband with his first major opportunity to demonstrate he can deliver votes in the ballot box.

Labour will certainly crow, if as expected, it gains control of Sheffield where Nick Clegg is an MP. But this and other possible gains in the North, such as Bolton, Oldham and perhaps even Leeds, will make less impressive headlines than gains further south, and especially gains made at the expense of the Tories.

However, the party is so weak in much of the South that such prospects look rather thin. But if outside chances of gains in Tory-controlled Gravesham and Thanet were realised, the party would reckon to have given David Cameron a bloody nose.

Meanwhile, with his party standing just one point lower in the polls than four years ago, the Tory leader will hope the losses his party suffers to Labour are compensated by gains from the Liberal Democrats. Not that that will make sustaining the Coalition any easier.

John Curtice is Professor of Politics at Strathclyde University