The Crown Prosecution Service has dropped one of its star expert witnesses after years of involvement in many criminal trials, BBC's Newsnight has learned.
Ms Rees' transcription of CCTV footage was used as key evidence against So Solid Crew's Shane Neil
Jessica Rees is the country's foremost forensic lip-reader and has been involved in high profile trials including one against members of the South London band, So Solid Crew.
She transcribes conversations captured on silent CCTV or surveillance tapes, working both for defence and prosecution lawyers.
Her evidence has been vital in putting people behind bars AND acquitting the innocent.
Ms Rees says she has been involved in over 700 cases and has lip-read more than 1,000 tapes.
But last year, her credibility was challenged in a case at Snaresbrook Crown Court.
A defence barrister Edward Henry accused her of misleading the court in her CV, which, he argued, suggested she had a degree from Balliol College, Oxford.
Ms Rees - who was the first completely deaf student to win a place at Oxford - readily conceded that she had not completed her degree. She said her CV was meant to show only that she had finished the first two years of the course.
The next day the Crown Prosecution Service dropped her as an expert witness in the Snaresbrook case. Mr Henry's client was later acquitted.
The police were asked to investigate Ms Rees on possible charges of perjury, and interviewed her under caution. The CPS has now decided not to prosecute her.
However, the CPS launched a review of her role and told Newsnight that "the Crown Prosecution Service has decided not to rely on Jessica Rees as a prosecution witness in current or future cases."
Retired Flying Squad detective Jim Crinigan describes Ms Rees as "absolutely fantastic"
They are also sending a disclosure package on events in the Snaresbrook case to lawyers involved in previous trials where Ms Rees has acted for the prosecution.
Jessica Rees has said she is surprised by the developments and insists that there was no intent to mislead the courts about her academic record.
There are also fierce arguments about the accuracy of lip-reading evidence. Ms Rees says her evidence is highly reliable. If she puts a word in a transcript, she says she is certain that it has been said. If the word is preceded by a question mark, she is 98-99% sure.
A retired Flying Squad detective, Jim Crinigan, who worked with her on a big robbery case at Heathrow Airport, describes Ms Rees as "absolutely fantastic."
Her transcriptions of surveillance tapes enabled the police to eliminate some suspects from their inquiry and to target the men who were eventually convicted of the robbery.
Shane Neil, a singer with So Solid Crew, has a very different opinion.
In 2003, he was charged with drugs and firearms offences. Another member of the band was arrested at the same time after running away and apparently discarding an illegal handgun.
The key evidence against Shane Neil was Jessica Rees' transcription of CCTV footage of the moments before and after the incident.
Shane Neil, who is seen waiting with other members of the band outside a London nightclub, removes an item from his sock. And later, according to the transcript he says; "do you want to buy a tablet?".
After police officers move in to search him, according to Jessica Rees, he then says "get rid of the ?gun [sic]" - which would demonstrate Neil had control of the weapon.
Another expert lip-reader challenged Ms Rees' transcription and told Newsnight she did not find the word "gun" on the footage. Meanwhile, the police found no other evidence of drug-dealing.
The prosecution decided to withdraw the lip-reading evidence and the case against Shane Neil collapsed. He is furious at Ms Rees' role in making him spend more than four months on remand.
"She should be sacked," he says. "Or she could be putting away more innocent men behind bars for something they never said."
Last year, the appeal court ruled in a separate case that lip-reading evidence should be admissible in principle, as long as the judge gives a warning to the jury about its reliability.
Jessica Rees maintains the accuracy of her transcriptions. "I have to be very confident indeed to include any words in the transcript," she says.
"And this only happens after an exhaustive process, which involves looking at sections of tape 40, 50, 60 times."
She told Newsnight she was surprised by the CPS decision because there was a full investigation during which she was cleared of all charges.
But it now looks as if her career as a prosecution witness could be over. However, she may still be able to work with police on surveillance work and on defence cases in court, which currently make up a third of her work.
The full report was screened by Newsnight on Monday 27 June 2005.
Newsnight is broadcast on BBC Two at 2230 BST every weeknight in the UK.