A promising new contraceptive injection that prevents men from fathering children is one step closer to being widely available after a two-year study found it to be 99% effective.

The testosterone jab, which is being dubbed as the male equivalent to the pill, is administered in the patient's buttocks once a month.

It works by regulating two hormones and blocking sperm production temporarily.

Chinese researchers claim that the jab has a higher success rate than condoms and provides an alternative to vasectomies, an operation that cannot be reversed.

The trial involved more than 1,000 healthy, fertile men aged 20 to 45, who were given monthly injections over a two-and-a-half year period.

All participants had fathered at least one child in the previous two years. Their female partners were aged between 18 and 38, and had no reproductive problems.

The hormonal injection produced better results than that of the pill, which fails one to two per cent of women.

The study, published in the Journal of Clinical Endocrinology and Metabolism, found that no serious side-effects were reported, and six months after stopping the jabs, all but two of the men's sperm counts were back to normal.

Dr Yi-qun Gu, from the National Research Institute for Fam­ily Planning in Beijing, said: "For couples who cannot or prefer not to use only female-oriented contraception, options have been limited to vas­ectomy, condom and withdrawal.

"Our study shows a male hormonal contraceptive regimen may be a potential, novel and workable alternative."

The Family Planning Association told the Metro: "This development is great news for men and women as it gives them more control over their sexual health."

Hormone birth control has been available to women for decades but often means that the onus is on the woman.

Despite this breakthrough, many experts are still encouraging the use of condoms to prevent the spread of STDs.

Diana Thomas, spokeswoman for family planning organisation Marie Stopes International, said: "We are pleased that there appears to finally be some sort of alternative for men than just the condom.

"But we would still encourage couples, especially those in new relationships, to make sure they're protected against STIs by using a condom."