Experts have called for written warnings before psychotherapy sessions, after recent research suggested that being asked to recall positive or negative aspects of childhood may affect how happy — or unhappy — a person recalls their childhood as being.

The team, from the University of Portsmouth, said their findings “could have implications for talking therapies that explore clients’ childhoods”.

In a study, they asked 301 participants to remember either a positive or negative memory of their mother, and a positive or negative memory of a teacher, or nothing at all.

The participants were then asked to rate how positive or negative their feelings were towards their mother and how happy they were in their childhoods.

Those who were asked to write a negative memory of