Nick Clegg refuses to give "running commentary" on the Lord Rennard allegations as the Lib Dems suffer their lowest-ever national poll rating less than two days before critical Eastleigh by-election.

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Pressure is mounting on the Liberal Democrat leader who is suffering some of his lowest poll ratings in wake of the Lord Rennard affair that has engulfed his party just days before the crucial Eastleigh by-election.

Detectives from the Metropolitan Police are due to meet senior officials today. Speaking outside his him in south-west London, Mr Clegg he said he understood there were "self-appointed detectives trying to piece together events that happened many years ago".

He said: "The only way that we are going to get to the bottom of the truth, the only way we are going to ensure that the women whose allegations were broadcast on television last week are properly listened to, the only way were are going to establish exactly what happened and who knew what and when, is by allowing the two investigations that I established immediately after the Channel 4 broadcast to do their job and, indeed, to allow the police, whom we have now approached, to do their job as well."

Liberal Democrat officials will today meet with detectives from the Met to discuss the allegations. It comes after Labour MP John Mann lodged an official complaint in wake of the allegations; a move he said was the "appropriate action to take".

Mr Clegg added: "I cannot and my party cannot provide a running commentary on every shred of speculation about events which happened many years ago."

Poll shock

The latest monthly poll by Comres for The Independent newspaper puts Nick Clegg in fourth place behind UKIP for the first time.

The survey, taken between Friday and Sunday when the fallout of the scandal dominated the news, is a further setback for Mr Clegg in the run-up to Thursday's critical Eastleigh by-election caused by the resignation of Chris Huhne.

There are, however, some positive signs ahead of Thursday's vote in Eastleigh. Signs suggest that the Lord Rennard story is not directly affecting voting intentions, with another poll suggesting a five-point lead for local MP Mike Thornton over his Conservative candidate Maria Hutchings.

Liberal Democrat officials will today meet with the Metropolitan Police to discuss the allegations. It comes after Labour MP John Mann lodged an official complaint in wake of the revelations, a move he said was the "appropriate action to take". Yesterday the party president Tim Farron admitted they "screwed it up as a party".

A Scotland Yard spokesman said: "The Metropolitan police special investigations command has been approached by officials in the Liberal Democrat party and is working with them to ascertain whether or not criminal activity has taken place."

Changing voter landscape

According to the Comres poll, which interviewed 1,005 adults, just one in three former Lib Dem voters would support the party now; whereas 40 per cent of them would support Labour.

Some 82 per cent of those who voted Tory in 2010 election would back the party now, although eight per cent say they would switch to UKIP now. According to the poll, Labour has retained the support of 92 per cent of its 2010 voters. If the data repeated on a uniform swing at a general election, the figures would give Labour an overall majority of 122. The Liberal Democrats would lose 39 seats, leaving them with just 18 MPs.

Lord Rennard denies the allegations, which predate Mr Clegg's leadership.