While men are more likely to chat up a fair-haired lady on a night out, they actually find brunettes more attractive, a study has shown.

University of Westminster researchers sent a woman to three London nightclubs with her hair dyed brunette, blonde and then red, and watched how many men approached her.

The researchers then returned to the clubs and asked 130 men to rate pictures of her in the three guises.

The woman was chatted up the most as a blonde. But she was rated most highly for attractiveness and intelligence when brunette, the Scandinavian Journal of Psychology reports.

University of Westminster researcher Viren Swami said that his results may reflect a shift in fashion, with brunettes now being idealized in the way that blondes were several decades ago.

Dr. Viren Swami said: “In the Sixties and early Seventies, when Jackie Kennedy was the ideal, brunette hair became the ideal for women generally. Then, in the Seventies and Eighties, blondes became the ideal.

“But more recently, there has been a backlash against blondes and the dumb blonde idea has become dominant.”

As a blonde, the woman was chatted up 60 times in total. This compared with 42 approaches as a brunette and 18 as a red-head.

Speculating on why the woman, or “confederate” in researcher-speak, was rated more attractive when brunette but chatted up more as a blonde, Dr. Viren Swami said: “One possible explanation is that men were more likely to assume sexual intent on the part of our confederate when she was blonde.

“Perceptions of the blonde confederate as being more needy may have reduced men’s fear or rejection or fear or an aggressive response, which increased their likelihood of approaching her as a blonde.”

It is also possible that men link blonde hair with youth and vitality, and so the ability to bear children.