Chris Huhne's ex-wife faces a retrial after a jury described by a judge as suffering "absolutely fundamental deficits in understanding" failed to reach a verdict in her case.
Vicky Pryce will stand trial again for perverting the course of justice as early as next week after the jury at Southwark Crown Court was discharged after saying it was "highly unlikely" it would reach even a majority verdict.
Mr Justice Sweeney said in 30 years he had never seen a situation like it after being presented with a list of 10 questions by the jury, after nearly 14 hours of deliberations.
They included: "Can a juror come to a verdict based on a reason that was not presented in court and has no facts or evidence to support it, either from the prosecution or defence?"
Discussing a possible solution, the judge said: "Quite apart from my concern as to the absolutely fundamental deficits in understanding which the questions demonstrate, I wonder, given that it is actually all there and has been there the whole time, the extent to which anything said by me is going to be capable of getting them back on track again.
"In well over 30 years of criminal trial I have never come across this at this stage, never."
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.
Mr Justice Sweeney gave the jury lengthy directions in a bid to answer their questions, but less than two hours later they said it was "highly unlikely" they would reach a verdict and were discharged.
Pryce, 60, of Crescent Grove, Clapham, south London, now faces a retrial, possibly as early as next week.
Huhne, who dramatically changed his plea to guilty on the first day of a joint trial with Pryce, resigning as an MP, will not be sentenced until the retrial is complete, the court heard. During the trial Pryce claimed a defence of marital coercion, claiming Huhne forced her to take speeding points for him nearly a decade ago, in 2003.