The Week in Politics: The fickleness of Labour's fair-weather fans

David Lammy, the health minister, wondered the other day why so many British people remain loyal to their football teams even when they do badly but "do not show the same loyalty with their political allegiances". As MP for Tottenham, the team I have supported in good times and bad, Mr Lammy should know what he is talking about.

David Lammy, the health minister, wondered the other day why so many British people remain loyal to their football teams even when they do badly but "do not show the same loyalty with their political allegiances". As MP for Tottenham, the team I have supported in good times and bad, Mr Lammy should know what he is talking about.

Although Labour looks the runaway favourite to win the premiership, its fans are disgruntled and the manager is worried that they will not bother to turn up for the crucial match on 5 May - only 100 days away next Tuesday. The reaction at Westminster to a Populus poll in marginal seats, pointing to another Labour majority of 160, was instructive. Labour MPs in marginal seats were jubilant. A week earlier, they had been running around like headless chickens, warning that the latest eruption of Blair-Brown divisions could cost them their seats. This week, they declared that the split merely showed Labour was "the only show in town."

You might think Labour leaders were delighted by the survey. The opposite was true. "It's bad news," one cabinet minister told me. "We are struggling to motivate our supporters, to make them fear the Tories. This makes it harder to get our people out when they think the Tories can't win."

Labour strategists fear that such polls will allow people who still identify with the party's values, but are fed up with Tony Blair, the luxury of abstaining or voting Liberal Democrat. As the parties' 100-day war gets under way, it is Charles Kennedy who has the ingredient politicians crave, what the Americans call "the big mo" - momentum.

The Liberal Democrats could be the main beneficiaries from the "can't win" syndrome that may afflict the Tories - the very problem that has dogged Britain's third party for years. Another Populus survey showed that, even though almost two out of three people are not happy with the Government, fewer than one in seven thinks the Tories will win. Nearly twice as many Tory supporters believe Labour is more likely to win than their own party.

Lord Rennard, the Liberal Democrats' number-cruncher and by-election guru, compiles a "poll of polls" and his latest report makes happy reading for Mr Kennedy. Six months before the 2001 vote, the monthly average showed Labour on 46.3 per cent, Tories on 32.9 and Liberal Democrats on 14.8. The main change between then and voting day was aswing of 4 per cent from Labour to the Liberal Democrats.

Last November, six months before the expected May election, the monthly average of the polls put Labour on 37.6 per cent, the Tories on 31.2 per cent and the Liberal Democrats on 21.6 per cent. A repeat of the pattern of 2001 this year would see all three main parties within eight points of each other. "The Liberal Democrats are starting on a much higher base, and the sort of momentum and tactical considerations that have applied in by-elections or in individual seats might start to apply nationally," says Lord Rennard.

The threat posed by Mr Kennedy's party is certainly being taken seriously by the two main parties. Although Labour and the Tories will portray the election as a "clear choice" between the only two parties who can win, they will both fight it as a three-way contest. Mr Blair, who privately describes the Liberal Democrats as "part of the social democratic family" and came close to a political marriage with them in 1997, has been persuaded that Labour must brand Mr Kennedy's party "soft on crime" and attack its plans for a 50p in the pound tax on earnings over £100,000.

The Tories hope the Liberal Democrats will unwittingly help them by allowing them to win a clutch of Labour-Tory marginals where Mr Kennedy's party is in third place but could attract disaffected Labour supporters. But the Tories sense the Yellow Peril spreading ominously in the many seats where they are being challenged by the Liberal Democrats.

However, a higher share of the vote for Mr Kennedy's party will not easily translate into seats under our first-past-the-post system. Some senior figures believe the best it can hope for is 20 more MPs, leaving it still a poor third in a two-horse race. In 1983, the recent high-water mark for the third party, the SDP-Liberal Alliance won 25 per cent of the votes but a paltry 23 seats. Labour won 27 per cent and got 209 MPs. Arguably, the bias in the voting system towards Labour is stronger today.

Mr Kennedy still has a lot of work to do. Given the unpopularity of both big parties, it is worth asking why the Liberal Democrats are not doing better. After calling Iraq right, have they missed their chance to become "the real opposition", as Mr Kennedy called them this week? Although his party has popular policies on pensions, free care for the elderly and university tuition fees, it needs to have a more distinctive message on health.

The election could be much closer - and more exciting - than the polls suggest. The fear in Labour circles is that the Tories will get their core supporters out and Labour won't. Differential turnout could make a huge difference. The Liberal Democrats' offer - a more effective Opposition in an inevitable Labour third term - will be an attractive one. Although only two parties can win, there is a third way.