Up to 20% of convicted criminals may have owned up to an offence they did not commit

Police need to be more aware of the danger of false confessions, according to a study that suggests that up to one in five convicted criminals may have pleaded guilty at some point to an offence they have not committed.

Gisli Gudjonsson, professor of forensic psychology at the Institute of Psychiatry at King's College London, said false confessions were a significant phenomenon of which the criminal justice system should be more aware. "Among people who are repeatedly arrested and actively involved in crime, a high proportion – 10% or 20% – claim to have made a false confession," he said. "If you study people in prison, something like 20% of them are saying they made a false confession in their life. They are much more common than previously thought."

Gudjonsson said his review of the available evidence relating to the psychology of false confessions suggests that high-profile miscarriages of justice involving murder or sexual offences represent the "tip of the iceberg".

A spokesman for the Criminal Cases Review Commission, which was set up to investigate miscarriages of justice, said it received around 900 applications a year, around 35 of which were referred to the court of appeal. "But obviously one miscarriage of justice is one case too many," he said.

The issue of false confessions and miscarriages of justice came to prominence recently with the case of Sean Hodgson, who in 1980, while in prison for theft, told a prison chaplain that he had murdered a barmaid, Teresa de Simone. He repeated the statement to a prison officer, but he was lying and in 2009, after 27 years in jail, he was released after DNA evidence proved his innocence.

Research in the US found that people had confessed to crimes they didn't commit in more than a quarter of convictions overturned by DNA testing. Gudjonsson, who is also head of forensic psychology services for Lambeth Forensic Services, says research is required to ascertain how many of the hundreds of thousands of interviews conducted by police in the UK each year contain a false confession. Gudjonsson will set out his views at a clinical forensics meeting next week at the Royal Society of Medicine in London.

Voluntary false confessions, he said, often arise from a pathological need for attention – usually notoriety – resulting from low self-esteem and feelings of inadequacy. But he said there was also a prosaic motivation for some false confessions: "taking on a case" in order to protect the real perpetrator. He said that around one in 10 14- to 16-year-olds in cases he studied claimed to have made a false confession to police, usually for minor offences. "It is quite common to take on a case for their mate, to protect their friend," he said.

Another factor can be police eliciting a confession – usually through a combination of interrogation techniques and the vulnerability of the suspect. "They might have a fear of detention and think that if they confess they will get out more quickly and hope that their lawyer will sort it all out," said Gudjonsson.

Police coercion and manipulative interrogation tactics can also play a role, although the interviewing techniques of UK police are much less likely to produce a false confession than those used in the US, where police take a more guilt-presumptive, confrontational approach.

A third factor leading to the prevalence of false confessions is health issues. "For example, a drug addict will go to the station and want to confess to get out as quickly as possible," said Gudjonsson.

He also cited research showing the tendency of attention deficit hyperactivity disorder and a disruptive childhood to predispose suspects to make false confessions.

However, Gudjonsson added: "It is a myth that only people with mental illness or learning disabilities make false confessions to serious crimes. Interrogators do on occasions elicit false confessions to serious crimes from normal individuals. Greater awareness and improved police interview training are important in reducing the risk of police-induced false confession."