A French survey found that nearly one in five impotent men successfully treated for the condition still did not have sex with their partner.

The problem is that women often refuse to have sex because they feel their partner's sexual urges are not natural, but have been artifically stimulated by chemicals.

Impotence consultants have said that women should be included in counselling and advice over treatment as a way to ease their concerns.

The survey results, published on the eve of the World Health Organisation's first conference on erectile dysfunction to be held in Paris, found that 91% of men of 50 responded to various anti-impotence treatments, including the drug Viagra.

But 17% of those for whom treatment worked still did not resume sexual relations with their partners.

Manifestation of desire

Viagra has helped many men

Dr Sylvian Mimoun, head of the fertility unit at Cochin Hospital in Paris, which conducted the survey, said that the involvement of women in consultations was essential.

He told a press conference: "When impotence first occurs, the woman generally plays it down and takes a wait-and-see stance, assuming that it is due to stress, fatigue or other reasons.

"That relieves both parties from guilt but does not resolve their difficulties."

He added: "The woman, and sometimes the man, considers the erection to be the manifestation of desire.

"That means that impotence is perceived as lack of desire. This disbelief must be corrected if treatment is to be helpful, otherwise the woman may attribute the return of post-treatment erections to chemical substances rather than to the man's desire for her, and may refuse sexual relations.

"If women aren't involved in treatment, in many cases they are not interested in the results."

UK has similar results

Dr Wallace Dinsmore, consultant at the Royal Victoria Hospital in Belfast, said he has seen similar results in the UK.

He said: "Just treating impotence in isolation as a medical problem does not work.

"Men who come to see me have often been impotent for three or four years.

"They may be successfully treated but after all that time, if they go home and say that they are cured and they want sex, their partners are quite likely to say 'no thank you'."

He added: "Women are more sensitive to the fact that their relationships may have deteriorated over the past few years and that there is more to the problem than the man simply not being up to the job."

But Dr Dinsmore said the launch of Viagra two years ago had led to an increase in the number of men coming forward and admitting they were impotent.

He said: "For years men did not think there was any treatment for their problems, but Viagra has become a brand name like Coca-Cola.

"Everybody knows now that treatments do exist. I saw one man last night who had been impotent for 25 years and has only just come forward because he heard about Viagra.

"Even if Viagra does not work, I can tell them about treatment which may work."

Since its launch, more than six million men in the US have taken Viagra, which has a 70% success rate.