The last time the Hampshire constituency of Eastleigh was plunged into a parliamentary by-election, the circumstances were even more bizarre than today's resignation by Chris Huhne on the steps of Southwark Crown Court. Stephen Milligan was a high-flying Tory MP whose political career had only just begun when, in 1994, he was found dead from auto-erotic asphyxiation.

The manner of his death intrigued and appalled the public, and sent the reputation of MPs – or of Tory MPs, at least – into freefall. When the Liberal Democrats destroyed a seemingly invincible Tory majority in the ensuing by-election, it was interpreted as a sign that the Conservative government was in terminal decline.

This time, it is the Liberal Democrats who have most to lose, – and Nick Clegg who has reason to fear the shattering impact that a by-election defeat could have on party morale. Their predicament looks dire. Though the Liberal Democrats have held Eastleigh in five successive parliamentary elections, it has never been a safe seat.

Huhne contested it for the first time in 2005, and only just scraped in by 568 votes. His majority went up to 3,864 in 2010, but he owed that increase in part to a tactical vote by Labour sympathisers wanting to keep the Tory out.

That tactical vote is unlikely to go their way again. Ray Finch, Ukip's organiser in Eastleigh, even suggests, optimistically, that the contest will be a "four-way marginal", with Labour and Ukip both in with a chance of taking at least 20 per cent of the vote.

It could yet prove to be a case of "a plague on all your houses" from a disenchanted public. The by-election is a problem that David Cameron does not need either, because the increasingly strident right wing of the Tory party will expect a victory, and blame Cameron if they don't get it. But the Conservative machine is weak on the ground. It has not won a council seat in the constituency since 2007.

There is also a question hanging over the Tory candidate – Maria Hutchings, one of David Cameron's "A-list" candidates, who fought Eastleigh in 2010 having no previous experience of politics, and has continued to call herself the "parliamentary spokesperson" for the Eastleigh Conservatives. She was not taking calls from journalists yesterday, but Charlie Daniel-Hobbs, a local Tory activist, said: "She has been leading the campaign here, she will want to be the candidate, and I think that will be taken into consideration by the local association."

Political rivals say that Ms Hutchings is a likeable person well qualified to be a local councillor, but suggest that party headquarters may try to install someone stronger for such an intensely fought by-election.

Keith House, the long-serving Liberal Democrat leader of Eastleigh council, had been preparing to take a week off active politics when the phone rang on Sunday night. It was Huhne on the line, to say that he was changing his plea to guilty. Until that moment, Cllr House had believed that Huhne would fight the charges and be acquitted. "My heart sank," he said. "It was not that I felt anger, or anything like that, but he's a hugely talented man and his departure is a massive loss. People in this constituency liked him and respected him, and are very sad."

It remains to be seen whether local voters will still be "sad" and not angry as the full details of Huhne's deception become known over the coming days. The Liberal Democrats have become accustomed to winning in Eastleigh. They hold every single council seat in the constituency, but now have to brace themselves against the possibility of a popular backlash.

"The Tories are not going to give us a walkover here, any more than Labour are," Cllr House said, "but there is no mood in the party of seeing this as doom and disaster. It's a very clear chance to show that the Conservatives and Liberal Democrats are two different parties."

Next in the hot seat? Ukip's Nigel Farage

Will he run, or will he hide? Nigel Farage, the public face of the UK Independence Party, says he will spend 48 hours thinking over whether to be his party's candidate in Eastleigh.

If he is, history will repeat itself. The first time Ukip fielded a candidate was in the 1994 Eastleigh by-election, and the candidate was the then-unknown Farage. Afterwards, he boasted narrowly beating Lord Sutch, leader of the Monster Raving Loony Party. "I've got to weigh up my responsibilities," Farage said on Monday night.

This time, he would need to give the Tory and Liberal Democrat candidates a close run if he is to look like a winner. But if he leaves it to his officer manager, Ray Finch, it may look like he has lost his nerve.