The man convicted of "menace" for threatening to blow up an airport in a Twitter joke has lost his appeal.

Paul Chambers, a 27-year-old accountant whose online courtship with another user of the microblogging site led to the "foolish prank", had hoped that a crown court would dismiss his conviction and £1,000 fine without a full hearing.

But Judge Jacqueline Davies instead handed down a devastating finding at Doncaster which dismissed Chambers's appeal on every count. After reading out his comment from the site – "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!!" – she found that it contained menace and Chambers must have known that it might be taken seriously.

He was also saddled with a legal bill three times higher than his original £384 with £600 costs, as the court ordered him to pay a further £2,000 legal bill for the latest proceedings.

Chambers, who lost his financial manager's job after his arrest in January, sent the message to a contact called @crazycolours, a young woman from Northern Ireland who was among 650 people who regularly followed his 140-character tweets.

They had arranged to meet in Belfast and Chambers told an earlier hearing he was desperate and frustrated that heavy snow might close Robin Hood, near Doncaster, and ruin their plans.

He used Twitter's private service to joke with her late at night about hijacking a plane, noting wryly that its pilots might expect to be diverted to somewhere more exotic than Northern Ireland. But his facetious bomb threat was sent on the network's public system, allowing anyone to see it – including staff at Robin Hood.

Chambers's conviction this summer caused huge controversy both on Twitter itself and among civil liberties lawyers because of its implications for the cyberworld's freewheeling style. The Crown Prosecution Service caused controversy by using a law aimed against nuisance calls – originally to protect "female telephonists at the Post Office" in the 1930s – rather than specific bomb hoax legislation, which requires stronger evidence of intent.

Judge Davies refused a request by Ferguson to cut the sentence to an absolute or conditional discharge. She effectively branded Chambers a liar by calling his denials about realising the possible implications of the tweet incredible.

She told the court that he had been an "unimpressive witness" and said: "Anyone in this country in the present climate of terrorist threats, especially at airports, could not be unaware of the possible consequences."

She also described some of his earlier evidence as "self-serving" and cast doubt on his claims not to have kept up to date with current affairs through newspapers or TV. As for the tweet at the centre of the case, she called it "menacing in its content and obviously so. It could not be more clear. Any ordinary person reading this would see it in that way and be alarmed."

Chambers and @crazycolours, who now live together in Northern Ireland, left court disconsolately and will now meet their legal team to consider a further appeal. The cost will be weighed against clearing Chambers's name and the wider issues, which have caused an international debate on social networking sites.

Chambers said he was also aggrieved at the heavy-handed handling of his case, saying that he had been held for seven hours in a police cell. He said: "I wouldn't have minded if they had told me off for being stupid, which was clearly how they saw things really, but it wasn't like that."

The wider implications were fanned by news of a second arrest under the same "nuisance call" law of a Conservative councillor in Birmingham who posted a tweet crudely attacking the columnist Yasmin Alibhi-Brown. The post by Gareth Compton, now removed, reportedly said: "Can someone please stone Yasmin Alibhai-Brown to death? I shan't tell Amnesty if you don't. It would be a blessing, really."

Compton, who represents Erdington on Birmingham city council, apologised after his release on bail and said: "It was an ill-conceived attempt at humour. I apologise for any offence caused. It was wholly unintentional."

The tweet was criticised in the House of Commons by the Leader of the House, Sir George Young, who was asked to allow an emergency debate by Steve McCable, Labour MP for Selly Oak in Birmingham.

Young said: "Stoning to death is a barbarous form of punishment which the government, and I am sure every member of this House, deplores. I hope that no elected person will threaten any member of our society with that form of punishment."