See what wonders a puce-faced minister will perform

Let's hear it for the choco-terrorist, the bosomy blonde Birgit who, with a little help from her friend Max Clifford, spread an eclair across Nick Brown's face and herself across the front page of every national newspaper. Only a farmer pitch-forking cow dung onto the Minister of Agriculture's podium could have provided a better photo-op at the National Farmers' Union Conference. As it was, the farmers were content to growl their protests while the politicians spun their policy; so Birgit Cunningham took gooey matter into her own hands and - splat! - pushed her cause (and herself) onto an unsuspecting nation.

Some cynics might argue that the cause closest to Ms Cunningham's heart was Ms Cunningham, rather than environmentalism, and that most of the photos and anecdotes supplied to the media in the wake of her pastry attack promoted Ms C's career somewhat more than the green agenda. We learnt a great deal about the socialite's LA drinking binges, her fling with Kevin Costner, and her striptease at a party. We saw photos of the busty blonde spilling out of her decollete, showing off her legs and pouting. The woes of intensive factory farming somehow got rather lost in this erogenous exhibitionism.

The farmers back home, steeped in their rural crisis and their traditional ways, must have found the in-your-face exploits of their self-appointed champion a tad embarrassing. But embarrassment is what publicity is all about - and what protest needs in order not to be dismissed as one nutter's hobby-horse.

If Brown had not been embarrassed by being covered with chocolate cream and if busty Birgit had not made an undignified spectacle of herself in the aftermath of her "direct action", the protest would have registered a lot lower on the Richter scale of public interest. The red face, the cringing expression, the stuttering: these are essential to the successful protest. When your opponents are public figures, the best means of making them mend their ways is not subversion, but out-in-the-open embarrassment. Public derision is the fastest shortcut to a politician's rethink.

This is a tried-and-tested method: pamphleteers in the 18th century knew that if you heaped scorn and ridicule upon a politician, you were more likely to achieve a government U-turn than if you merely criticised his policy. Protesters such as Mahatma Gandhi and Nelson Mandela did not, it must be admitted, resort to throwing pastries at their enemies, or pelting them with rotten eggs; but they, too, named and shamed their opponents into puce-faced embarrassment - and then, reform.

The more authoritarian the regime, the more its leaders detest losing face. Protest, whether it is manning the barricades or pulling a vaudeville stunt, becomes all the more potent and all the more dangerous - just look at the Chinese reaction to being shown up by students in Tiananmen Square.

Embarrassing the powers that be may not prove as lethal in Tony Blair's Britain, but being put on the spot is equally dreaded by the new Labour apparatchiks, who set greater store by their public face than their inherent principles. With ministers and minions obsessed with losing face, and so terrified of losing popularity, the canny protester can turn embarrassment into a sure-fire tool for change. Trip up and catch out a Mandelson, Campbell or Blair and you will reduce the government to its knees. New Labour men and women will walk miles away from the line they draw in the sand in order to avoid having egg on their face.

In campaigning terms, all publicity is good publicity. In political terms, that just ain't so - just ask Ron Davies, Jeffrey Archer et al.

So farmers should rejoice. With her well-aimed lob, their self-appointed champion has embarrassed a minister. They couldn't have hoped for a better way to force their cause onto the government's agenda. Unless, of course, that pitchfork of manure . . .