Study shows how false memories rerun 7/7 film that never existed

Four out of 10 people have false memories of the 7/7 London bombings, according to researchers who questioned students about what they remembered seeing on news reports of the events.

Some people claimed to have seen non-existent CCTV footage of the bus exploding in Tavistock Square in July 2005, while others gave detailed descriptions of footage which did not exist.

The study shows how prone people are to "false memories", which the researchers say police and social workers must take into account when evaluating witness testimony or "recovered" memories of childhood abuse.

"Taken as a whole, this is further evidence that our memories are not perfect," said Dr James Ost, a psychologist at the University of Portsmouth. "They are not like a videotape you can rewind and replay for perfect recall. Because of this, memory alone is not reliable enough to form the basis of legal decisions."

He gave questionnaires to 150 British students and 150 Swedish students on what they remembered of the Tavistock Square bomb three months after the attacks. None had seen the bomb first hand. He asked the students what they remembered about TV footage of the aftermath of the bomb and about CCTV images of the bus exploding and a computer reconstruction of the event.

Neither the CCTV or the computer reconstruction existed, but 40% and 28% of British respondents claimed to remember seeing them. The equivalent figures of the Swedish participants were 16% and 6%.

Some of the students embellished their accounts with details they could not have witnessed. One wrote: "The bus has stopped at a traffic light. There was a bright light and a loud bang and the top of the bus flew off."

The study backs up previous research by Ost in which people claimed to have seen non-existent footage of the crash in Paris that killed Princess Diana.

Ost presented the research at the British Association Festival of Science in Liverpool.