A teenage juror, who interrupted a trial when he pretended to be ill so that he could go and see a London stage show, has been detained for 14 days, the Judicial Communications Office said on Thursday.

Matthew Banks, 19, could now spend Christmas in a young offenders institution after he told officials at Manchester crown court he was too poorly to turn up at the trial he had been attending.

The court proceedings were then halted for a day and the remainder of the jury was sent home. But Banks went to see the show Chicago in the West End.

The university student was found out and brought before the judge Martin Rudland, who labelled him "frivolous" and ordered that he serve two weeks in a young offenders institution.

The week-long trial later continued in the absence of Banks, with the remaining 11 jurors reaching a verdict, officials said.

Rudland said he was locking up Banks "with a heavy heart" but added that lying to court officials for such a frivolous reason was a serious offence.

The teenager's mother, Debbie Ennis, 49, from Staffordshire, described the sentence as "ludicrous", and vowed to appeal and get her son home for Christmas. "He's a naïve 19-year-old and when he told me what happened, we told him to hold his hands up and apologise, because we trusted the British justice system. He wanted a career in the government but he's got a criminal record now. We thought he'd get a slap on the wrists."