I've previously looked at the cabinet ministers who could provide this election's "Portillo moment", but which Tories and Lib Dems are under threat?

Few on the Tory front bench need fear for their seats, but several are still vulnerable to the Liberal Democrats. Oliver Letwin, the Tories' policy director, will have to watch his back in West Dorset, where he is defending a notional majority of 2,461.

Elsewhere, David Mundell, the Tory shadow Scottish secretary and the party's only Scottish MP, enters the campaign with a majority of just 1,738 in Dumfriesshire, Clydesdale and Tweeddale. He will be challenged by Labour, which held the seat until 2001.

Others who will be campaigning hard include the shadow culture secretary, Jeremy Hunt, who is defending a notional majority of 5,981 in Surrey South-West, and Theresa Villiers, who holds a notional majority of 5,556 in Chipping Barnet.

But it's the Lib Dems who have most to worry about on polling day. Chris Huhne, the party's home affairs spokesman and runner-up to Nick Clegg in the last leadership election, is defending a notional majority of just 530 in Eastleigh and is number 11 on the Tory target list.

Meanwhile, owing to boundary changes, Sarah Teather's Brent East seat no longer exists. She now hopes to unseat the Labour MP Dawn Butler in Brent Central but will have to overturn a majority of 6,608.

Others who could be swept away by a large Tory swing include Tim Farron, the party's environment spokesman, who has a notional majority of 846 in Westmorland and Lonsdale (267 under the old boundaries), and David Heath, MP for Somerton and Frome, whose seat is now notionally held by the Tories.

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