About 150,000 people a year are failing to turn up for court appearances in England and Wales, the Magistrates' Association has said.
New methods are being used to try to improve court attendance
The Metropolitan Police Federation called the situation "a disgrace" and said the law needed to be changed to prevent defendants not attending court.
Fears have also been raised that the situation is undermining confidence in the criminal justice system.
The Home Office said it was meeting its targets to combat non-attendance.
The Magistrates' Association said 8.2% of people did not turn up for their trial in magistrates' courts in 2006. Magistrates deal with about two million cases a year.
The Home Office said that 2.2% of trials failed to complete in the financial year to December 2006 because of defendant non-attendance.
The figure has fallen from 5.6% in the financial year 2002 to 2003.
Experts said there were a number of reasons why people did not turn up - from deliberately defying the courts, to people simply forgetting when they were due to appear.
Theft victim Kathryn Allen was asked to attend the trial of the alleged thief as a witness, only to see it collapse when he did not turn up.
She said she was shocked at the extent of the problem.
"I don't know if next time I would agree to be a witness because it seems to me that I've been the one that's been put out and not him at all," she added.
Glen Smyth, chairman of the Metropolitan Police Federation, said officers were frustrated at the numbers of those escaping trial.
"This happens time after time in courts up and down the country and it is a disgrace," he said.
He called for a change in the law to make it easier for officers to keep those charged with offences in custody before they appear in court.
He also said defendants should appear in court sooner and said a US-style system where money is put up in exchange for bail should be considered.
A multi-agency Home Office group has been set up, the Defendant Attendance Steering Group, to look into the problem.
John Thornhill, a member of the group and deputy chairman of the Magistrates' Association, said non-attendance was an "important" problem.
"Effectively unless magistrates decide to deal with the case there and then there are extra delays," he said.
"Which means problems for victims, if there are any, and witnesses. There are also cost implications because it means finding another court on another day."
He added: "If people see, the public particularly, defendants don't turn up it will undermine their confidence in the criminal justice system."
Mr Thornhill said courts were using new methods to improve attendance such as texting, phoning and emailing defendants to remind them of court dates.
A Home Office spokeswoman said outstanding Fail to Appear warrants had been reduced by 48% since 2004 and they were on course to achieve the March 2007 target.
She said a National Enforcement Service would be rolled out from April, which will focus on enforcement action against those who flout court orders and those who fail to turn up.