Disastrous national opinion polls are having little effect on a crucial Westminster by-election, the Liberal Democrats claimed yesterday, ahead of a visit by Deputy Prime Minister Nick Clegg to the campaign trail.

The party is hoping that the appeal of its leader will help them win the Oldham East and Saddleworth seat, which they failed to take in May by just 103 votes amid an election campaign that ended in controversy.

Liberal Democrats believe the contest can buck a trend in declining support seen across the rest of the country, as the party takes the blame for unpopular coalition policies such as increased university tuition fees.

A clutch of senior LibDems visited the Oldham East and Saddleworth seat yesterday, including Norman Baker, the transport minister, Paul Burstow, the health minister, and Steve Webb, the pensions minister.

They followed Business Secretary Vince Cable and former party leader Charles Kennedy, while today will mark Mr Clegg's second visit to the seat since the by-election was called.

The election contest is one of the most unusual in recent years. It was called after a court ruled that Labour's general election victory was invalid because the former immigration minister Phil Woolas had misrepresented his rival, LibDem Elwyn Watkins, trying to inflame racial tensions.

It is also the first by-election in which the new coalition partners are ostensibly fighting each other, although there have been suggestions that the contest has perhaps been more "gentlemanly" than previous encounters.

And the result could be extremely close between all three parties – while the Lib Dems lost by just over 100, the Tories were also less than 2500 behind them, not insurmountable in this kind of contest.

However, the Liberals are acutely aware that their public support has collapsed dramatically.

One recent poll put them as low as 9%, a steep fall from the heights of more than 30% that they enjoyed at the height of the "I agree with Nick" fervor during the pre-election televised debates.

The spate of low scores in opinion polls have led observers to predict that the party will get trounced the next time the public has a chance to voice its view.

But party insiders claimed yesterday the Oldham by-election could buck that trend.

A source said: "The issues that are important on the doorsteps here are local issues like the decline of manufacturing.

"There is also a lot of anger about Phil Woolas and the way he behaved.

"If you look at the national polls, people say that Labour are going to walk it, but that is not at all what is happening on the ground."

Mr Clegg's visit follows on the heels of an appearance by Labour leader Ed Miliband, who campaigned in the constituency earlier this week.

Aides to Mr Miliband confirmed yesterday they expected him to visit the seat again at some point before next Thursday's election, which will also be seen as a key test of his leadership of the Labour Party since his election last September.

David Cameron is also expected to take to the campaign trail at some point later this week.