A man found guilty of sending a "menacing tweet" was the victim of a legal "steamroller" that threatened to make the law look silly, it was argued at the High Court.

Paul Chambers, 27, said he thought that no-one would ever have taken seriously his joking threat to blow an airport "sky high".

Accountant Chambers said he sent the tweet to his 600 "followers" in a moment of frustration after Robin Hood Airport in South Yorkshire was closed by snow in January 2010. But he was convicted at Doncaster Magistrates' Court of sending "a message of a menacing character", contrary to provisions of the 2003 Communications Act, fined £385 and ordered to pay £600 costs.

He asked two High Court judges to overturn a Doncaster Crown Court decision in November 2010 upholding his conviction and sentence - a decision which pushed the costs order against him up to £2,600. Among his many supporters are fellow "Twitter comedians" Charlie Brooker and Stephen Fry.`

Crown Court Judge Jacqueline Davies, sitting with two magistrates, said the electronic communication was "clearly menacing" and that airport staff were sufficiently concerned to report it. She added: "We find it impossible to accept that anyone living in this country, in the current climate of terrorist threats, would not be aware of the consequences of their actions in making such a statement."

At London's High Court, Ben Emmerson QC, appearing for Chambers, argued the Crown Court had erred in law - and in common sense. Mr Emmerson suggested it was hardly likely that anyone planning to blow up an airport would post their intentions on Twitter.

He told Lord Justice Gross and Mr Justice Irwin that conviction and sentence were normally meant to have a deterrent effect, but in the Chambers' case they had the opposite effect. His conviction caused resentment and triggered an "I am Spartacus!" campaign in which 4,000 people tweeted the Chambers message across Twitter - "none of whom were arrested", said Mr Emmerson.

Robert Smith QC, for the Crown Prosecution Service (CPS), disagreed. He said the tweet was not viewed as a joke by those responsible for airport security. It was posted at a time when the potential terrorist threat to airport security was high.

The judges reserved their judgment and said it would be handed down at a future date.

Among those sitting at the back of the court supporting Chambers were Pub Landlord comic Al Murray and Father Ted writer Graham Linehan. Mr Murray, who recently hosted a special benefit performance for Chambers, said outside court: "I defend everyone's right to tell rotten jokes. This situation is Monty Python. It is absurd, bonkers. It means we cannot post what we want on Twitter, or say what we want - that is incredible to me."