He was a courting lover who ended up with a criminal conviction after saying on Twitter he would blow an airport "sky high" if it wasn't reopened to let him fly to see his new girlfriend in Northern Ireland.

Paul Chambers, a 27-year old trainee accountant from South Yorkshire, today launched a fightback against what is thought to be the UK's first criminal conviction for the content of a tweet on the microblogging site.

He landed a £1,000 fine after the snow closed Robin Hood airport near Doncaster in January as he planned a trip to see "Crazycolours," a Northern Irish girl he had just met online, and he tweeted to his 690 followers: "Crap! Robin Hood airport is closed. You've got a week and a bit to get your shit together otherwise I'm blowing the airport sky high!!"

A week later, he was arrested at work by five police officers, questioned for eight hours, had his computers and phones seized and was subsequently charged and convicted of causing a "menace" under the Communications Act 2003.

In an appeal at Doncaster crown court, his barrister, Stephen Ferguson, said Chambers had been merely engaging in "banter and craic" and that far from having menacing intent, his message was "a jest, a joke, a parody".

In an extraordinary day's evidence the court heard arguments ranging from the fundamental right to the freedom of expression, to the emerging nuances of Twitter etiquette and an often painstaking exposition of the basics of social networking for the two magistrates and Judge Jacqueline Davies who were presiding.

At one point the defence even appeared to ask the court if the criminal justice system would treat Sir John Betjeman in the same way as Chambers if it was considering his most famous verse. "Part of the importance of this case is that if this tweet is somehow of menacing character, so would countless others from the playground to Twitter users across society, day by day," said Ferguson. "To misquote Betjeman: 'Come friendly bombs drop on Slough.' The point is an obvious one."

The defence applied to the judge to rule out the prosecution case that the tweet was "menacing" on the grounds it had not been sufficiently proved and there was no intent on Chambers' part to cause menace. Throughout proceedings, Chambers sat largely expressionless behind toughened glass panels with a security guard beside him, only wincing slightly at the the continual repetition of his offending tweet. He nodded when Ferguson told the judge simply: "The intention was innocent."

On the other side of a glass barrier in the public gallery sat Crazycolours, the pseudonym of the Northern Irish woman who only gave her name as Sarah, with whom he had been planning to meet. "Young love did spring from these tweets and he is now living in the same country as Crazycolours," the court was told.

Fresh evidence emerged which was not heard at the previous trial that the police noted after Chambers was bailed "there is no evidence at this stage this is anything other than a foolish comment posted on Twitter for only his close friends to see". But the crown said the conviction should stand and presented evidence that Chambers had sent direct messages to Crazycolours apparently on the terrorist theme.

Caroline Wiggin, for the prosecution, said Chambers had earlier sent direct messages to the woman in Northern Ireland as it appeared possible that the airport might close. In one he wrote: "I was thinking if it does I have decided to resort to terrorism." She argued that the context provided by such messages strengthened the case that Chambers intended to cause menace. "If a man in prison were to send a message to his wife that he was going to come and beat her up, the court might consider that were menacing, albeit the man himself may have difficulty in putting it into effect," she said.

Ferguson argued that Chambers's messages were obviously "hyperbolic banter" and served to reinforce the fact that he was joking in the main message which he sent to all his followers about blowing up the airport. "This [message] is obviously facetious," he said. "There are at least three exclamation marks. The first to add to the slightly naughty word 'crap'. The last two to the parody of 'to blow the airport sky high'." The court earlier heard that a senior airport official had "determined [the message] was a non-credible threat" after it had been found by Sean Duffield, an off-duty airport duty manager searching on-line at home. Under cross-examination, Duffield, said the impact after he found Chambers' message was "operationally nothing. It had no impact."

Chambers was not cross-examined, but the court heard extracts of his original police interview. "Looking back it's daft now but that's my kind of humour," Chambers had said. "Not for one second did I think anyone would even look at it. It was just a comment made on the back of the fact that the flight had been grounded." The tweet, Stephen Ferguson pointed out, was made in the context of "a young man and a young woman".

The judge and magistrates retired to consider their ruling and said the case would conclude a later date.

Facebook terrorism

In a case with echoes of Chambers' trial, US standup comedian Joe Lipari also landed in court on terrorism charges following an outburst on Facebook over the state of his iPhone.

He bought the phone a year ago and, after it repeatedly crashed, took it back to the Apple Store in Manhattan. They tweaked it, it crashed again, and the next day he went back to get a replacement. After waiting hours he stormed home with no replacement and, while watching Fight Club, updated his Facebook status in parody of a cherished line from the film: "Joe Lipari might walk into an Apple store on Fifth Avenue with an Armalite AR-10 gas powered semi-automatic weapon and pump round after round into one of those smug, fruity little concierges."

In no time at all plain clothes police armed with MP5 machine guns were knocking on his door. It didn't help that he had been smoking dope and found the whole scene hilarious, amusement that continued into court, where he was charged with making terrorist threats.

His case is currently adjourned and expected to be dropped.

Maev Kennedy