Twitter joke trial: what you need to know

A man who received a conviction for tweeting a joke about blowing up a snowbound airport takes his case to the high court today.

Paul Chambers is contesting the criminal sentence he received in 2010 for sending a "menacing communication".

He is arguing that his tweet was clearly a joke and not a serious threat.

His cause has attracted high-profile support from campaigners and celebrities, including the actor and broadcaster Stephen Fry and the comedian Graham Linehan.

The outcome of the case could influence the way similar investigations and convictions are conducted in the future.

Here's the background to what has become known as the "Twitter joke trial".

Why is the case so significant?

Because it is believed to be the UK's first criminal conviction for the content of a tweet.

How did it all start?

The affair dates back to January 2010 when Paul Chambers sent the following tweet to his followers:

An airport security manager found the tweet on a random search of Twitter. He wasn't sure whether it was a joke or not, and referred it to his manager, who graded it as having no credibility. But the manager was duty-bound to forward the tweet to the airport police.

One week later Chambers was arrested by five police officers, questioned for eight hours and had his computers and phones seized.

After interviewing Chambers, the police said there was no evidence that the tweet was anything more than a joke intended just for his Twitter followers. However they passed any charging decision on to the Crown Prosecution Service.

Chambers was subsequently charged and convicted of causing a menace under section 127 of the Communications Act of 2003.

What does the act say?

The act states it is an offence to send:

Chambers' solicitor, David Allen Green, has argued that the 2003 act was only used because the Crown Prosecution Service "realised there was insufficient evidence of intent for the 'bomb hoax' offence under the 1977 Criminal Law Act." He adds that: "the CPS used the then obscure section 127 of the Communications Act, for which there are no recorded cases other than in respect of nuisance telephone calls, and baldly asserted that the provision now covered communications on social media as well."

What were the consequences for Chambers?

Chambers, a trainee accountant, was found guilty by magistrates, handed a £1,000 fine and lost his job.

Did he appeal against the sentence?

Yes, but the decision was upheld in September 2010 by a judge and two lay magistrates at Doncaster crown court. This prompted the launching of a fundraising campaign to help Chambers fight the sentence and, if necessary, take the case all the way to the high court.

Who got involved in the campaign?

Various high-profile celebrities. Stephen Fry, Al Murray and Graham Linehan were among those to offer financial support. A fundraising show was staged in April 2011 to raise more money.

Several journalists have also commented on the case, largely to highlight what they believe to be the absurdity and worrying significance of the conviction, including Charlie Brooker at the Guardian and Nick Cohen at the Observer.

What are Chambers' lawyers arguing in his defence?

All along Chambers and his team have said that his tweet was not intended to menace the airport authorities and was "a jest, a joke, a parody".

They state that the imposition of a fine and criminal record breaches his rights to free expression under the European convention on human rights.

Back in November 2010, Chambers' solicitor David Allen Green wrote that:

Chambers is being represented by Ben Emmerson QC, of Matrix Chambers, who specialises in freedom of expression cases and European human rights law.

What happens if Chambers loses his case?

His criminal conviction will stand and he will retain a criminal record. He may also have to pay the legal costs of the other side.