As Sally Bercow names a teenager on Twitter whose identity is protected by a court order, and Lord McAlpine's lawyers pursue those who defamed him in tweets, what next for the social network?

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It was already a Twitter storm - now it could become a full-blown hurricane.

Thousands of Twitter users who falsely branded Lord McAlpine a paedophile are facing legal action after the peer's lawyer, Andrew Reid, warned: "We know who you are".

One of those facing legal action, the Speaker's wife Sally Bercow, may since have landed herself in even more hot water on Twitter on an entirely separate issue, with a tweet which could identify a schoolgirl whose identity is protected by law because of her age.

Last night, Ms Bercow tweeted asking what had happened to a teacher who allegedly ran off with a schoolgirl earlier this year. The teacher was arrested in France in September and was last week remanded in custody after appearing in court charged with the abduction of a 15-year-old child.

Even the birds in my garden seem unusually quiet. Frightened to tweet lest somebody sues them, I guess. Krishnan Guru-Murthy

A court order prevents the publication of the girl's name because of her age, but Ms Bercow revealed it last night on Twitter, then adding: "Forgive random question - just discussing with friend."

A report today in the Daily Telegraph suggested that the tweet counted as publication, putting the Speaker's wife - who has almost 60,000 followers - potentially in breach of the court order and in line for a £5,000 fine.

Sarah Webb, a media lawyer with Payne Hicks Beach, told the paper: "The contempt of court requirements will apply to her just the same as any newspaper or broadcaster.

"I would advise her to be very cautious. I would certainly urge her to turn off her Twitter account at the moment."

"Is that fair? It's probably not fair, but as my dad said to me, life's not fair. Ignorance of the law is no defence and it never has been," said Mr Chapman.

"It's not fair that people have been able to say these things in a bar either - and actually that's never been the case, that's always been slander. The fact is that now, when you are communicating to a wider audience, you are much more likely to be caught out."

He said he expected more and more claims to be brought over the content of tweets and also predicted that increasing number of companies would start laying down guidelines to highlight what their employees can and can't do on Twitter - regardless of whether they use the "all thoughts my own" disclaimer.

"The fact is that some people should just know better...What we are seeing is that people like the FA are introducing a code of conduct for footballers. There isn't a group representative of the average Twitter user - but they should be encouraged to use a little bit more self control," he said.

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Green cross code?

Mrs Bercow is far from the only person to fall foul of the law on Twitter, and the two latest scandals are hardly the first to be broadcast all over the social network - remember super-injunctions?

But many are now suggesting that the sheer numbers who face action as a result of naming Lord McAlpine in the wake of the BBC's Newsnight falsely accusing a "senior Thatcher-era Tory", coupled with the increasing regularity of "trial by Twitter" situations, could make this a game-changer.

Channel 4 News Presenter Krishnan Guru-Murthy, an early adopter of Twitter, wrote in his blog: "Even the birds in my garden seem unusually quiet. Frightened to tweet lest somebody sues them, I guess."

David Aaronovitch and Charlie Brooker have both written advice columns in the Times and the Guardian about how best to use the social network. Alex Chapman, head of interactive media at London law firm Sheridans, told Channel 4 News this could be the future for Twitter.

"The advice for everybody who uses social media should just think about it and not say something on a public forum that they wouldn't want to be broadcast.

Ignorance of the law is no defence and it never has been. Alex Chapman, head of interactive media, Sheridans

"Lawyers are told to never write a letter or an email that they wouldn't want a judge to read out in court. Lawyers are trained like that, and while Joe Public hasn't had that training, when they are on the road they look both ways before crossing.

"Maybe it's time for a green cross code for using social media. Maybe there is a moral responsibility on the providers of these services to educate users - but that would be much less fun," he said.

Twitter itself is not legally liable for what appears on its site, as the law sees it as merely a platform rather than a publisher - that is, until the company is put on notice that something unlawful is going on. At that point, it has to act to remove the content.

As such, it is really up to the person tweeting to think before they tweet - particularly on legally dubious issues - because they are effectively publishers and so need to think about all aspects of the law, from contempt to libel.

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