'Twitter joke' case only went ahead at insistence of DPP

The director of public prosecutions (DPP) stopped his staff dropping the case against Paul Chambers, author of the "Twitter joke" about blowing up Robin Hood airport in South Yorkshire, it has been claimed.

Crown Prosecution Service lawyers had been prepared to back away from one of the most controversial cases in years, telling Chambers that they no longer saw a public interest in opposing his appeal against conviction. Chambers had said he felt "immense relief" that the prosecution – which had seen him lose two jobs and gain a criminal record – appeared to be over and that the authorities seemed ready to restore his good name.

The CPS even sent Chambers and his solicitor, free-speech campaigner David Allen Green, papers stating that it now agreed that the case should end. However, at the last minute the DPP, former human rights lawyer Keir Starmer, overruled his subordinates, it is alleged.

In January 2010, Chambers had booked a flight from Robin Hood airport to see his girlfriend in Northern Ireland. Bad weather forced the airport to cancel flights and he tweeted to his 600 followers: "Crap! Robin Hood airport is closed. You've got a week and a bit to get your shit together otherwise I am blowing the airport sky high!!"

South Yorkshire police officers arrested Chambers at his workplace and his employers sacked him. The CPS decided to charge him with sending a message "of a menacing character". On 10 May 2010, Doncaster magistrates found Chambers guilty. He then began a succession of appeals.

Chambers told the Observer he was "bitterly upset" at Starmer's decision to prosecute.

He said: "Mr Starmer was prepared to put me through the worry of yet another hearing, waste yet more taxpayers' money and waste the time of the lord chief justice." The case went ahead and the high court found in Chambers's favour on Friday and overturned his conviction.

The prosecution provoked protests around the world. Comedians led by Stephen Fry and Al Murray defended the right to make bad jokes. Twitter users staged mass protests online and well-wishers funded the appeal.

Friends of Chambers said Starmer was trying to save face by refusing to admit he was in the wrong. Louise Mensch, Chambers's MP, has called on the Commons home affairs or justice committees to investigate the DPP's behaviour.

A CPS spokesperson denied Starmer was a decision-maker in the case and insisted he did not overrule his subordinates. The spokesperson said that conceding the appeal had been a consideration at one stage but this was not possible because only the high court could overturn a crown court finding.

The CPS confirmed that it spent £18,000 fighting Chambers at a time when the criminal justice system was struggling to cope with cuts in funding. Taxpayers will also have to pay Chambers's costs.