Media playback is unsupported on your device Media caption The BBC's Clive Coleman says it was "a highly unusual day in court"

The jury trying Chris Huhne's former wife Vicky Pryce has failed to reach a verdict on a charge relating to speeding points she took for the ex-minister 10 years ago.

Ms Pryce, 60, of Clapham, London, faces a retrial before a new jury on Monday.

She denied perverting the course of justice, saying Huhne, who pleaded guilty, had coerced her in 2003.

The judge said some of the questions from the jury had shown a "fundamental deficit in understanding" of its role.

Mr Justice Sweeney was speaking after a list of 10 questions was sent to him by the jury on Tuesday as its deliberations continued at Southwark Crown Court.

Speaking in court later on the same day in the jury's absence, the judge said: "In 30 years of criminal trials I have never come across this at this stage, never."

He also criticised the jury's lack of understanding of the trial process.

Basic duties

Earlier this month, Huhne, 58, had admitted perverting the course of justice and resigned as Liberal Democrat MP for Eastleigh in Hampshire.

Analysis It is not uncommon for jurors to ask questions of the judge, even late on into their deliberations. What's so unusual in this case is the number of them, 10, and their very basic nature which reveal a fundamental misunderstanding of their role as jurors and of the judge's directions. It is extremely rare for a judge to comment on a jury's "deficit in understanding", as Mr Justice Sweeney has done. Such words are reserved for truly exceptional cases. In recent years judges have made huge efforts to make their instructions clear. They're schooled in clarity and their directions are now routinely supplied to the jury in writing. However, today is a reminder that there can be a real deficit in language and understanding between judges and lawyers, and the jurors they address. Talking about things such as the "burden and standard of proof", and a wife's will being "overborne" by her husband, might seem to be clear. But whilst no one is suggesting that judges put everything into layman's terms, a balance has to be struck between legal language and clear, unambiguous, words that every juror can understand.

He and Ms Pryce, an economist, were charged over an incident in March 2003 when his car was caught by a speed camera on the M11 between Stansted Airport, in Essex, and London.

It is alleged that between 12 March and 21 May 2003, Ms Pryce falsely informed police that she had been the driver of the car so that Huhne, then an MEP with hopes of becoming an MP, could avoid a driving ban.

During her trial, Ms Pryce accepted that she had taken Huhne's points, but she adopted a defence of marital coercion, claiming he had made her sign a form he had already completed in her name.

The jury had asked the judge questions about its basic duties after about 14 hours of deliberations and lengthy advice from him about how to assess the evidence.

The questions included seeking a definition of reaching a verdict "beyond reasonable doubt" - something the judge had given them in writing.

In another question, the jury asked if one of them could come to a verdict based on reasons that were not presented in court or supported by the evidence. A third question asked about Ms Pryce's religious convictions, even though this was not a matter in the trial.

On Wednesday, Mr Justice Sweeney gave them a majority direction, saying he would accept a verdict on which at least 10 of the 12 jurors agreed.

'Fairly unique'

But later he received a note from them saying it was "highly unlikely" they would be able to reach a majority verdict.

This is not jury misconduct, this is not irregularity, this is a jury which has not, it appears, understood its function Andrew Edis, Prosecutor

He then told the jury: "Against the background of the length of time that you have been in retirement already, I have decided therefore, and it is my decision one way or the other, that I must discharge you from any further deliberations."

Prosecutor Andrew Edis QC said the jury of eight women and four men did not appear to have "truly understood" or "sufficiently grasped" its task.

"I don't ever recollect getting to this stage in any trial, even in far more complicated trials than this one, and, after two days of deliberations, a list of questions of this very basic kind illustrating that at least some jurors do not seem to have grasped it," he said.

It was a "fairly unique situation" in which the jury had sent a note containing 10 questions aimed at attempting to understand the fundamental purpose of their presence, he said.

"This is not jury misconduct, this is not irregularity, this is a jury which has not, it appears, understood its function," he added.

Sentencing of Huhne, who could face a prison sentence, will take place after the retrial of his former wife.

A by-election is being held in Eastleigh on 28 February to find a replacement for Huhne.