Feminine charm is a measurable phenomenon, scientists have established, with women who employ it enjoying the most success in negotiations.

Results from the first academic study of the technique shows that it can increase success rates in negotiations with both men and women by as much as a third.

Effective feminine charm combines flirtation with friendliness and women who get it right can get around 20 per cent off the price of a car, according to the study.

But getting the right balance between flirting and being friendly is vital, because women who are too straightforwardly friendly lose out, according to Dr Laura Kray who led the study. "They are seen as pushovers; as caring solely about satisfying other people's interest. We found that flirtation, on the other hand, conveys assertiveness and power, from someone who is also concerned about satisfying their own interests," she said.

Researchers from the University of California, Berkeley, and the London School of Economics, carried out four separate experiments to investigate female charm. They say that, while there is a commonly held assumption that feminine charm boosts a woman's effectiveness in negotiations, it has not until now been investigated by researchers.

It is defined as a management technique available to women that combines warmth, friendliness, and affiliation with flirtation, including playfulness, flattery, and sexiness. The character Joan Holloway from TV's Mad Men is considered an effective user of the technique. Real-life examples include Maria Fe Perez-Agudo, president and chief executive of Hyundai Asia Resources Inc and Susan Lyne, chair of Gilt Group.

"Feminine charm is a strategic behaviour aimed at making the person you are negotiating with feel good in order to get them to agree to your goals,'' says Dr Kray. The report claims former US Secretary of State, Madeleine Albright used feminine charm in bilateral talks.

Researchers believe the evolutionary roots of the technique lie in the Catch-22 situation women face in many day-to-day negotiations. In order to succeed in a male-dominated world they have to adopt a masculine style, which is not liked. But failure to do so makes them appear less competent. Feminine charm allows women to mitigate the antipathy aroused by their male-like behaviour when negotiating.