Continuing my look at the seats that will illustrate how well or how badly each party does at the election, here’s my pick for the Liberal Democrats.

As with my list for Labour, each of the six seats below represents a particular kind of contest, the result of which will serve as a measure of the Lib Dems’ success – or failure.

1. Solihull

Conservative target no. 3

This is the Liberal Democrats’ most marginal constituency in the country. Lorely Burt is defending a majority of just 175, and the Tories need a swing of 0.2% to gain the seat. It should change hands easily, but it will be the size of the Conservatives’ victory that will be worth watching. If the Tory candidate Julian Knight takes Solihull by a huge margin, ending up with a majority of around 5,000, the Lib Dems could well be in for a very bad election. But if Knight manages only a narrow win, Nick Clegg’s party may end up holding on to more marginals than expected.

2. Sutton & Cheam

Conservative target no. 19

The Tories need a swing of only 1.7% to overturn Paul Burstow’s majority of 1,608. Yet I suspect he may survive. Burstow has a very strong local following, and the Lib Dems performed well in this part of London in the local elections of May 2014. Polls have suggested he will hold on, and if he does it will be a model example of individual Lib Dem MPs bucking the nationwide trend and defying the odds. If Burstow wins again and even increases his majority, it will signal the Lib Dems are fighting back in some areas and that their performance in the election across the UK could be markedly inconsistent.

3. Cornwall North

Conservative target no. 49

Dan Rogerson’s majority here is only 2,981, but the Tories need a 3.2% swing to defeat him. If they manage it, the Liberal Democrats could be looking at losing around a third of their MPs. Cornwall North is one of the Tories’ more ambitious targets. It is not one of the Lib Dems’ most perilous seats. The party has held it continuously since 1992. If they lose it in 2015, Nick Clegg will be steeling himself for a very poor election.

4. Birmingham Yardley

Labour target no. 54

This will be a test of how well Labour is doing in picking off its Lib Dem targets. John Hemming achieved a majority of 3,002 in 2010, and the seat would change hands on a swing of 3.7%. Labour ought to be able to win here, but a poll published by Lord Ashcroft in late November put the Lib Dems ahead. If Birmingham Yardley remains out of Labour’s grasp, Ed Miliband will have failed to make the kind of advance into Lib Dem seats that he needs to offset potential losses elsewhere, and which is necessary for his party become the largest in the new parliament.

5. Bermondsey & Old Southwark

Labour target no. 104

A real Labour long shot. If Simon Hughes is defeated here, Labour will be having a bumper night at the Lib Dems’ expense. Hughes has a majority of 8,530; Labour’s candidate Neil Coyle needs a swing of 8.6% to take the seat. I’ve yet to see any poll or trend that suggests Hughes is at genuine risk, but it’s the sort of place ripe for a shock result and a historic election upset. The Lib Dem vote would need to collapse massively in Coyle’s favour, however.

6. Caithness, Sutherland & Easter Ross

Possible SNP target

The Liberal Democrats have 11 MPs in Scotland. How many might be at risk from a resurgent SNP is hard to predict, but if John Thurso loses in Caithness, Sutherland & Easter Ross, things will be looking grim. In 2010 Thurso managed a majority of 4,826 over Labour, with the SNP coming third. But the nationalists were only 6,391 votes behind the Lib Dems. An SNP victory here would be a marker of how well the party is profiting from a sink in support for its centre-left rivals. It would also imply the Lib Dems could lose as many as half of its Scottish seats.