Primary colours

Guardian Unlimited Politics | Special Reports | Primary colours: "Labour has unveiled its latest weapon in the battle against the Tories - a bicycling chameleon called Dave. But will the charge that the Conservative leader changes his views stick? And do political adverts work in any case? Tania Branigan reports"

Political advertising is a confusing business. The list of successful ads - most famously, Labour isn't Working, the campaign credited with helping to propel Margaret Thatcher to power in the 1979 general election, is matched by those that have rebounded on their authors, notoriously, the Tory Demon Eyes campaign, which depicted a pair of red, devilish eyes peering out from Tony Blair's face and also, in another related ad, from behind a red curtain. To many voters, it summed up the negativity and nastiness that they associated with the Conservatives.

The party's last general election campaign slogan, meanwhile, "Are you thinking what we're thinking?" also provoked charges of nastiness.