Can you be so Yes that you help No?

Can you be so No that you help Yes? The two official independence referendum campaigns - as they fuss over their final message grids - face the same challenge: how to limit the damage inflicted by their own most zealous fringes.

For Better Together, the problem comes draped in an orange sash and sporting a bowler. Scotland's noisiest Unionists, already registered as referendum participants, are to march on the eve of the big vote. The pro-UK camp is trying to stop traditional working-class Labour voters, many of them with Irish Catholic roots, from turning to Yes. Does it need a big parade by sectarian loyalists? "No Thanks." Does it need fired-up leaflet donkeys? Well, perhaps. That is the dilemma of dealing with radical grassroots: mainstream campaigns need their brawn, not their bile.

Yes Scotland has its extremists too. They may not be as politically toxic as the Orange Order but, increasingly, campaign insiders regard them as every bit as counter-productive. Why? Because, unlike the Order and Better Together, they badge themselves as mainstream Yes.

Last weekend -and some independence supporters will hate me for saying this - Yes had its Orange Order moment, an act of PR suicide. Hundreds of independence supporters picketed the BBC Scotland HQ at Glasgow's Pacific Quay. Their grievance? What they see as Aunty's "bias". There were kilts, there were Saltires and there were placards calling Aunty's journalists liars. And there was official Yes merchandise, despite no official Yes endorsement.

Better Together could barely contain its glee. First came the social media jokes about tin-foil hats and MI5 conspiracies. Then came the press releases. Labour's Jim Murphy saw the protest as a sinister attempt by supporters of a government party to "bully broadcasters".

Unfairly conflating the picket with mainstream civic nationalism, Mr Murphy added: "More and more Scots are looking at their angry and divisive campaign and finding it a turn-off." Controversial? Surprisingly not. SNP thinkers agreed. "It would turn me off, if I was undecided," said Paul Togneri, a senior party communicator, of the BBC picket.

Former heads of PR at both Yes Scotland and Scottish Greens made the same point online. Such protests, they said, make Yes look like it was a sore loser blaming the referee. Angry about bias? Go and hit some doorsteps, they suggested. They cited rule number one: Don't shoot the messenger, even if you really, really feel he or she deserves to be up against a wall.

How did some of those who supported the demo respond? Well, Mr Togneri and his fellow critics were blocked on Twitter. Social media, after all, is where Yes grassroots organise. It is also where their anger erupts as - in another suicidal PR tactic - they badger journalists and celebrities. Yes leaders - accused, surreally, of orchestrating such Twitter mobs - cringe and try to channel the anger into positive campaigning, gently reasoning with some of the more obtuse websites. It doesn't always work. "They don't understand movement politics," said one Yesser of Yes HQ. "We are grassroots, not astroturf."