THE Prime Minister has refused to commit himself to visiting Norwich to help his party in the critical by-election that will be held in Ian Gibson's old seat on July 23.

THE Prime Minister has refused to commit himself to visiting Norwich to help his party in the critical by-election that will be held in Ian Gibson's old seat on July 23.

Asked yesterday in Downing Street whether he was planning to go to the city to boost the Labour campaign, Gordon Brown initially dodged the question. When it was repeated, he tetchily emphasised: “I am not commenting on that at the moment.”

A defeat for Labour in the by-election could trigger another attempt to replace him as his party's leader. And a decision by him to keep out of the campaign will be interpreted by the opposition parties as a sign that he is anticipating the loss of the seat and will try to dissociate himself as much as possible from an electoral humiliation.

There has long been a convention that prime ministers do not participate in by-elections, but it is broken when they feel like it. Mr Brown twice campaigned in last year's by-election in Glenrothes, and his wife Sarah spent a lot of time in the constituency.

The Prime Minister embarks today on a regional tour of England that will take him to Yorkshire, the North East, the North West and the Midlands, but will exclude East Anglia.

He was also non-committal yesterday when asked whether he accepted that Dr Gibson had been treated unfairly by Labour's 'star chamber' disciplinary machinery. After praising the former MP “for the work he did for Norwich”, he said the party's disciplinary system that de-selected him - over his second home allowance claims - “is what it is”.

He refused to take a further question about the by-election. And his apparent reluctance to go to Norwich produced an accusation from Mid Norfolk Tory MP Keith Simpson that “it looks as if he is running away from the by-election”.

Mr Brown later endorsed his party's Norwich North candidate, Chris Ostrowski, as someone “absolutely on the side of hard-working people, He will tackle the big issues that people in Norwich care about, like anti-social behaviour and cleaning up politics, and will back more investment in the services that people need, like teachers and sure start children's centres.”

But Labour's decision to have an early poll in Norwich North seems to be inspired by an expectation of defeat and a calculation that it is best to get the bad news out of the way as quickly as possible. In the Glasgow North East seat of former Commons Speaker Michael Martin, which Labour is confident of winning, a by-election is not expected until November.

Dr Gibson retained his seat at the 2005 general election with a majority of 5,459, with the Tories in second place. And with national polls giving David Cameron's party big leads, and against the background of local unhappiness over Dr Gibson and his de-selection, Tory candidate Chloe Smith is a clear favourite to beat Mr Ostrowski and gain the seat.

The Liberal Democrats, Greens and UKIP are also confident, however, that the troubled political backcloth will also help their candidates, and that they could run Labour close.

Norwich North is a traditional Labour seat - although it was held by Tory Patrick Thompson for 14 years up to Dr Gibson's first win in 1997 - and defeat in the by-election would set many alarms ringing again in Mr Brown's party.

The contest will he held two days after the Commons goes into its long summer recess, and the date will also have been fixed with that in mind. MPs will not be able to gather in Westminster corridors immediately after a Labour defeat to start plotting the PM's downfall again.

The choice of a date after the Commons had broken up showed that Mr Brown was “running scared” said Tory campaign manager Theresa May.

To gain Norwich North, the Conservatives need a swing from Labour of 5.8%. That is a modest requirement compared with the 17.6% swing they obtained last year to gain the Crewe and Nantwich seat.