Jonathan Reed: Clegg's campaigners aim for double city conquest

Labour has held Hull North for 46 years but Nick Clegg has long spoken of his intent to wrestle it away in a city where the Liberal Democrats have taken a grip on the city council in recent years. A healthy Labour majority has failed to deter the Lib Dem challenge in Sheffield Central where former Sports Minister Richard Caborn is standing down.

In Hull, the Lib Dems are certainly winning the poster war where Junior Schools Minister Diana Johnson is contesting Denis Healy.

But Lord Norton, Professor of Government at the University of Hull, says high visibility is a traditional Lib Dem tactic and does not necessarily mean support is soaring . He suspects Labour may be pushed close but end up hanging on.

"On paper, it's an uphill struggle for the Lib Dems – it would take about a 12 per cent swing," he says. "But given the state of the polls, obviously that's given them renewed hope."

Clegg and his deputy, Vince Cable, have campaigned in the seat to signal their intent. The fact that it includes some of the city's student population gives them further hope.

However, this is a seat with a long Labour tradition that takes in Bransholme, one of Europe's biggest council estates.

It has been held by Labour since Henry Solomons won it from the Tories in 1964, and when he died less than two years later Harold Wilson was so desperate to keep hold of it to keep his wafer-thin majority the Government announced funding for the Humber Bridge to be built during the by-election, with Barbara Castle declaring: "You shall have your bridge."

Ironically, one of the issues Mr Healy is campaigning on is for the the bridge's 350m debt to be written off by the Government so the tolls can be scrapped.

Some claim Kevin McNamara's victory in the January 1966 by-election persuaded Mr Wilson to call a General Election weeks later – although he insisted he had already decided the date – where he won an increased majority.

One thing that could have an impact on winning the seat this time is turnout, with low voter participation a regrettable feature of Hull democracy.

Over in South Yorkshire, boundary changes – which bring the wards of Broomhill, Nether Edge and Walkley fully into the seat – are working in the Lib Dems' favour by knocking an estimated 2,000 votes off Labour's majority. Like in Hull, they are operating a high visibility campaign.

As council leader, candidate Paul Scriven has the advantage of a high profile but the disadvantages that go with making unpopular decisions.

With Mr Caborn's retirement, Labour candidate Paul Blomfield, husband of Euro MP Linda McAvan, is seeking to portray himself as the change candidate insisting the Liberal Democrats are not the fresh faces they are in other parts because of their control of the city.

Just as David Cameron battles with Mr Clegg to be the leader who offers the best prospect of electoral change, the battle in Sheffield Central could come down to which of the men wins the contest to seize the mantle of change.

THE FACTS: HULL NORTH

Current MP: Diana Johnson, Labour

Notional majority: 7,384

Last election: Swing 6.3% Lab to Lib Dem

Confirmed candidates:

Conservative – Victoria Aitken

Labour – Diana Johnson

Liberal Democrat – Denis Healy

BNP – John Mainprize

English Democrat – Michael Cassidy

Green – Martin Deane

UKIP – Paul Barlow

Rating: Uphill battle if Lib Dems are to win

THE FACTS: SHEFFIELD CENTRAL

Current MP: Richard Caborn, Labour (standing down)

Notional majority: 5,025

Last election: Swing 9.1% Lab to Lib Dem

Confirmed candidates:

Conservative – Andrew Lee

Labour – Paul Blomfield

Liberal Democrat – Paul Scriven

BNP – Tracey Smith

Green – Jilian Creasy

Independent – Rod Rodgers

UKIP – Jeffrey Shaw

Rating: Fierce fight between Lab and Lib Dems