Iain Duncan Smith has been dealt a fresh poll blow with the news that Charles Kennedy's Liberal Democrats have closed the gap on the Conservative Party.

Following last week's Brent East by-election, where the Tories were pushed into third place, the Lib Dems are just two points behind the official opposition.

While Labour stands at an 11-year low of 35 per cent, Kennedy's party has increased its standing by six points to 28 per cent.

That puts the Lib Dems just two points behind the Conservatives - who polled 30 per cent in the ICM/Guardian survey.

If this performance was repeated at a general election, a number of key shadow cabinet members would lose their seats.

Those targeted by the Lib Dems include party chairman Theresa May, local government spokesman David Davis and shadow home secretary Oliver Letwin.

But the poll also makes grim reading for a government still damaged by the Iraq war. It finds that a majority of voters now believe the conflict was unjustified.

Some 53 per cent saw no justification for the military campaign, compared to just 38 per cent in favour of the action.

The rating represents a dramatic fall in support from a 63 per cent high in April.

The shift in opinion follows a failure to find weapons of mass destruction and a raft of revelations from the ongoing Hutton inquiry.

Liberal Democrat voters were found to be most hostile to the war - with a net justified/unjustified rating of minus 45 points.

There has also been a fall in support among Conservative voters - from plus 20 in July to minus 12.

Although Labour supporters remain in favour of the military action, support has fallen over the last three months from plus 30 to plus 16.

And Labour's woes were not solely confined to the Iraq war.

Only 29 per cent of voters named the government as the party with the best policies for the economy, compared to 47 per cent in March.

The poll came as the prime minister sought to play down the government's recent difficulties "I totally understand why parts of the media are very interested in the Hutton inquiry - that will go on," he said on Tuesday.

"But meanwhile we have got to do the things that matter to the people of the country - the NHS, education, crime, asylum, these are things that matter to the people of the country.

"By elections will come and go but the most important thing is to make these changes."