A good time for Tories to vote Liberal Democrat

By-elections were once the engine drivers of the political process between general elections

The Brent East by-election tomorrow could have a catastrophic outcome for both Tony Blair and Iain Duncan Smith. The biggest winner is likely to be apathy, but if the stay-at-homes can be persuaded by the Liberal Democrats to go to the polling station, Charles Kennedy may have to dust down that speech by his predecessor but one, David Steel, about going "back to your constituencies and prepare for government", in time for next week's Brighton party conference.

There was a period when by-elections were regular engine drivers of the political and parliamentary process between general elections. Tory by-election defeats during the 1992-97 parliament steadily reduced, and then wiped out, the Government's majority, to the extent that by January 1997 John Major's government actually became a minority administration. Such by-elections were a tale of woe for the Tories, as they lost a clutch of safe seats, mainly to the Liberal Democrats. They continue to this day to retain seats gained by this process, such as Newbury and Eastleigh.

By-elections often have the power to change the political landscape. Few doubt that it was the loss of Eastbourne to the Liberal Democrats in the autumn of 1990 by the Tories that became the ultimate catalyst in the demise of Margaret Thatcher. The IRA murdered the sitting member, Ian Gow, that summer. The parliamentary party blamed the loss of Eastbourne on the poll tax, and became terrified that unless drastic action was taken against Mrs Thatcher the consequences would be defeat for the Tories at the subsequent general election.

Similarly, the loss by the Tories of Newbury, in May 1993, to the Liberal Democrats was said to be the final straw for Norman Lamont's career in government. Mr Lamont had struggled on as Chancellor of the Exchequer since Black Wednesday the previous September, but he was fired from his post by John Major just three weeks after the drama at Newbury.

Since Labour won power in 1997, however, by-elections have had less of an impact on the political process. The Labour government's huge majority - and comparative popularity in mid-term - have meant that the parliamentary arithmetic remains unaffected by by-election results. During Mr Blair's first term, not a single Labour seat was lost. Ironically the only change was in Romsey in 2000, where under William Hague's leadership the Tories lost the seat to the Liberal Democrats.

In recent times, there have been far fewer by-elections than in previous parliaments. The vagaries of the grim reaper seem to suggest that MPs are younger and fitter than in previous times. The average age of MPs has fallen since the huge influx of new MPs in 1997. Older Tory MPs lost their seats to generally younger Labour replacements (I lost my seat at the age of 46 to a 37-year-old Blair Babe).

So it is a cruel irony that there is even a by-election at all this Thursday in the safe Labour seat of Brent East. The sitting member who has died, Paul Daisley, was elected for the first time at the age of 44 in 2001, and he took over from the 56-year-old Ken Livingstone, who did not seek re-election after his election as Mayor of London. Mr Daisley's vote of 18,365 represents 63 per cent of the vote. His Tory rival got 5,278, and the Liberal Democrat 3,065.

By all the parties' canvass accounts, the Tories look certain to be beaten by the Liberal Democrats into third place. This will be a gloomy backcloth to the Tory party conference, and there are already signs of yet another bout of leadership speculation, with Tory MPs resuming their plotting.

As usual, the straw in the wind is Michael Portillo. In his latest TV appearance - and there have been several these past few days - he suggested that IDS is destined to lose the next election, unless there is a "once in a generation upset". While Mr Portillo does not expect there to be a leadership challenge, his remarks will give encouragement to those who do.

But if the Tories are destined to come third in Brent East, perhaps their supporters should make the best of a bad situation and help ensure that the even bigger headline on Friday morning is a Labour defeat by the Liberal Democrats.

I have no hesitation in saying that, if I were a Tory voter in this constituency, I would hold my nose and vote Liberal Democrat - playing the kind of tactical vote game that Labour supporters did so cheerfully in Romsey, where the party's vote of nearly 10,000 in 1997 slumped to 1,451 in the by-election in 2000. There was little doubt that Labour voters in Romsey cared little that they lost badly. They recognised that the value to them was the bigger headline of the Tory loss of the seat.

The Liberal Democrats' spokesmen are rightly being coy about their chances. They have learnt over many years not to go beyond saying "it's very tight"; but William Hill is offering odds of 6-5 joint favourites on both Labour and Liberal Democrats, which shows how close this race could be. Tory voters hold the key to defeating Labour in a by-election for the first time since Tony Blair was elected. This key could unlock the door to far greater turmoil inside the Labour Party and presage the end for Mr Blair.

mrbrown@pimlico.freeserve.co.uk