The memories of witnesses are flawed, marred by gaps or inventions and should not be relied upon in court cases, researchers say.

Memories are a record of people’s experiences of events – not a record of those events themselves, their report concludes. People also “remember” events that they have not in reality experienced and such recollections could – if heavily relied upon – lead to wrongful convictions.

Memory and the Law is being published today by the British Psychological Society, along with guidelines to help those in the legal system to evaluate evidence based on memory. It recommends that courts use memory experts to help juries to evaluate memory-based evidence where, for instance, given by a child or elderly person.

Martin Conway, of the University of Leeds, the report’s main author, said: “Without corroborating evidence, witness testimony based on memory should not be relied on. In many legal cases, memory may feature as the main or only source of evidence, and it is nearly always critical.”

It was difficult, if not impossible, for jurors to know how accurate a memory was likely to be, he said. “What we say is that there is really not such a thing as a true memory. It is a record of experience – but is your experience a true record of reality?”

The memory would lose details and have gaps, would be modified and changed by subsequent recall and could conflate events or experiences.

The report says that memories dating from below the age of 7 cannot be relied upon without independent evidence. Memories of specific events after the age of 10 can be highly accurate, highly inaccurate or wholly false.

A memory of a traumatic event such as being in the Second World War could be highly accurate decades later, the report says, as could vivid memories of one’s circumstances when hearing of a big news event, such as Margaret Thatcher’s resignation. “Set against this are findings, for many of the same events, of wholly false memories and memories that are partly accurate but which contain clearly false details.”

Professor Conway cites a middle-aged man who had a vivid memory of his father talking to him about the first man on the Moon. His father had been on the telephone to his mother, who had just given birth to his brother. Only decades later did he realise that his brother was born one year before the Moon landings.

“The event probably did occur but on a different occasion and has been transposed in memory,” the report says. “This does not necessarily entail deliberate deception.”

In the criminal justice system, witnesses’ memories of events might be influenced by the way they were questioned, Professor Conway added. He cautioned particularly against reliance on memories of younger children, older adults and other vulnerable groups, as well as those with memories of traumatic events. “Older adults are more prone to false memories because of an overreliance on the gist of an event.”

With children, memory of events before the age of 3 should not be accepted without corroborating evidence, and memories of events from 3 to 5 should be “viewed with considerable caution”, the report says.

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