Nick Clegg on the campaign trail in Oldham

Nick Clegg, deputy prime minister and leader of the Liberal Democrat party, during a visit to Asda supermarket in Oldham Photograph: Dave Thompson/PA

Nick Clegg talks to shoppers at Asda supermarket in Oldham Photograph: Dave Thompson/PA

A protester gets close to Nick Clegg as he and the Liberal Democrat candidate for Oldham East and Saddleworth, Elwyn Watkins, second left, arrive at a supermarket in Oldham Photograph: Paul Ellis/AFP/Getty Images

Deputy prime minister Nick Clegg is heckled by student Jennifer Leah as he talks to voters at Asda supermarket ahead of the Oldham East and Saddleworth byelection Photograph: Christopher Furlong/Getty Images

Nick Clegg with candidate Elwyn Watkins canvassing in Diggle Photograph: Dave Thompson/PA

Nick Clegg and candidate Elwyn Watkins speak to a resident in Diggle Photograph: Dave Thompson/PA

Nick Clegg comes to the aid of Elwyn Watkins as they are confronted by Greenpeace activist Peter Mellor (right) in Diggle Photograph: Christopher Thomond for the Guardian

Nick Clegg and Elwyn Watkins, the Lib Dem candidate for Oldham East and Saddleworth, campaign for votes in Diggle Photograph: Christopher Furlong/Getty Images

Nick Clegg out and about in Diggle Photograph: Dave Thompson/PA

Nick Clegg addresses members of the public during a visit to Saddleworth museum Photograph: Christopher Furlong/Getty Images