John Curtice: This is a calamitous result for Brown

Analysis

About as bad as expected – that is, close to being calamitous. The result from Norwich North provided further evidence that Labour is staring general election defeat in the face.

At 16.5 per cent, the swing to the Conservatives was almost on a par with the 17.5 per cent the Tories secured in capturing Crewe & Nantwich last year. Prior to Crewe, they had not inflicted so bad a by-election defeat on Labour since the darkest days of the 1970s Labour government. Now, little over 12 months later, they have repeated a feat that suggests David Cameron is on course for general election success.

True, there was one big difference between Norwich and Crewe. The swing reflected a collapse in the Labour vote rather than a dramatic Conservative advance. At just over six points, the increase in the Tory share was quite modest, well down on the near-17-point advance in Crewe. Perhaps this should give the opposition leader a moment's pause?

Modest though it might have been, the increase in Conservative support was still the third highest in any by-election since 1997. And they have registered their increase despite a continuing anti-Westminster mood.

Ukip's 11.8 per cent share of the vote was their highest ever in a by-election. Although the Greens might feel disappointment at conceding fourth place, their 9.7 per cent was also their highest ever by-election share. These two performances come in the wake of the record 40 per cent of the vote secured by non-Westminster parties in last month's Euro-elections. Although recent opinion polls have identified some decline in support for "Others", at an average of 16 per cent their standing is still unusually high.

In truth, all three main Westminster parties will be anxiously looking to see whether the expenses scandal has given the smaller parties a boost that outlives the Euro-contest.

At nearly 27 points, the decline in Labour's share of the vote was one of the worst it has suffered since 1997. Previous losses on this scale – Hamilton South (1999), Brent East (2003) and Birmingham Hodge Hill (2004) – occurred in previously safe Labour seats in the wake of third party insurgencies. This disaster occurred in the kind of key Labour-Conservative marginal where the national battle for power at the next general election will be won and lost.

Doubtless, Labour will argue that local circumstances played their part in Norwich – the controversial sacking of the locally popular MP, Dr Ian Gibson. Of course that was no isolated local incident, but the product of Gordon Brown's handling of the expenses scandal. His decisive action was meant to benefit his party. Instead, it seems that once again events have uncovered the Prime Minister's lack of political touch.

John Curtice is Professor of Politics at Strathclyde University