Leading article: Wit and popular wisdom

You have to feel a bit sorry for the political parties and their PR agencies. No sooner have they devised their latest masterpiece of persuasion, airbrushed the party leader to their satisfaction, and posted the resulting triumph of medium and message on to the hoardings, than along comes a crowd of cynical, tech-savvy voters on their computers and their mobiles, intent on making a mockery of the whole thing.

Any sympathy, though, should quickly give way to delight in the sheer wit and ingenuity of the alternative poster brigade. Here we have the British at their irreverent best, harnessing the potential of the new media to add their two-ha'pence worth to the national conversation. Who said the voters were disengaged? The fate of David Cameron's NHS poster suggests they are rather more engaged than the party PR people might like. Maybe they should sign up a few of the i-Banksys in a defensive capacity? Better still, let a hundred virtual flowers bloom.