Leading article: This yellow surge is good for democracy

The "Black Swan" of this general election has turned out to be the yellow bird of the Liberal Democrats. The traditional third party of British politics has surged quite remarkably and utterly unexpectedly since last week's first television debate between the three main party leaders, to the extent that the polls are now putting them ahead of Labour and some even have them outstripping the Conservatives.

Those who are weary of Gordon Brown's Labour, yet still unenthused by the Tories, appear to have discovered a new force that merits their support. Nick Clegg's achievement in that historic debate was apparently to tap into the yearning of the British public for a break with the discredited political status quo.

And there is no reason to assume this is merely a temporary phenomenon. Success often breeds success in politics. The once potent accusation that a vote for the Liberal Democrats was a waste looks ever more ridiculous as successive polls show them making progress. And the more coverage the party gets in the national media, the more people take them seriously.

This Liberal surge has left the Conservatives in severe difficulties. David Cameron wanted to position himself as the "change" candidate. Instead, Mr Clegg has usurped his position. It will be hard for Mr Cameron to attack Mr Clegg from the illiberal right without undoing his own efforts to present himself as a different sort of Conservative leader. Yesterday Mr Cameron was reduced to arguing that a vote for the Liberal Democrats would result in four more years of Mr Brown. The trouble is that this relies on too many assumptions about the distribution of seats in a hung parliament and what would result from subsequent negotiations. Furthermore, it hardly represents a positive reason to vote Conservative.

Labour, too, is unsure too about how to respond. The Liberal Democrat surge benefits them in many seats in the South-west and the South and Mr Brown has been trying to hug the party close, so as to benefit in the event of a hung parliament. But beyond a certain point, rising Liberal Democrat support begins to hurt Labour too, especially in their northern heartlands.

Despite the difficulties of the Conservative and Labour high commands in responding to the Liberal Democrat challenge, the two parties' friends in the media are beginning to attack the party's policies on crime, Europe and immigration. The Liberal Democrats' policy platform is certainly not perfect. Scrapping university tuition fees is a regressive measure. And while the Liberal Democrats go further than the other parties on how they would tackle the deficit, they do not go far enough.

Yet on civil liberties, immigration, criminal justice, on working with our European neighbours and reducing our national carbon emissions the Liberal Democrats have an impressively progressive and logical platform. Consider the Liberal Democrats' proposals for voting reform. If the most recent polls were translated on polling day, Labour would end up with the lowest share of the votes but the most seats. This is so manifestly ludicrous that even the most stubborn Tories must surely be starting to recognise the iniquity of the present first-past-the-post system.

Of course, the yellow surge might fade as the campaign progresses. But even if it does, this Black Swan has already served to inject further excitement and uncertainty into this election. The essence of democracy is uncertainty about who the people will choose to govern. Certainty is the friend of the well-connected and the vested interest. We certainly have a great deal of uncertainty now. Thanks to the Liberal Democrats and Mr Clegg, this election has come truly alive.