Academics from the University of Southampton looked at women in Britain and France and found that finishing full-time education and training at an older average age is the main reason why people are having their first child later in life.

Professor Maire Ni Bhrolchain, who conducted the study with Dr Eva Beaujouan, said: "A large number of explanations have been suggested for the trend towards later parenthood, but our study is the first to show that the major influencing factor is that people have been staying on longer in education and training."

The average age of a woman having her first child in 2004 was 27, while the average was 24 in 1974, according to the study called Fertility Postponement and published in the journal Population Studies.