The humble tapeworm could be the source of a new form of contraception for both men and women, researchers say.

A tapeworm found in fish contains a chemical compound that appears to make the fish infertile.

It seems to interfere with the fishes' hormone production, so females do not produce eggs and males do not produce sperm.

Researchers from Keele University say this chemical could form the basis of a contraceptive for humans that both men and women could use.

The chemical could provide a new form of contraception

But they stress any Pill is years away.

The tapeworm, Ligula intestinalis, is found in freshwater fish in the carp family.

It suppresses the production of eggs and sperm by interfering in the function of the pituitary gland.

Toad research

Professor Chris Arme, of the Centre for Applied Entomology and Parasitology at Keele, who has spearheaded the research, told BBC News Online: "Fish are vertebrates and we are vertebrates, and though our endocrine and reproductive systems do differ in important ways, they do have important similarities, particularly in the hormonal areas."

"Our hypothesis was that if it does this in fish, it might do it in other vertebrates."

Tests were carried out on toads, and found that the tapeworm had the same effect.

Professor Arme says he does not yet know what the chemical in the tapeworm is which is responsible for the contraceptive action.

Further research to isolate the compound are planned, and also to see if it also occurs in mammals.

Professor Arme said he believed the effect of the chemical would be reversible.

He added: "The tapeworm contraceptive may yet come to occupy a place in our medicine cupboards.

"But, in contrast to the products currently available, this could be labelled 'For him or for her'."

The research was published in the journal Biologist.