A male contraceptive jab more effective than the Pill has been found to prevent pregnancy for up to two years.

Contraception options for men have not changed in a century, remaining limited to condoms or the more drastic decision to have a vasectomy.

But an injection which blocks sperm from leaving the body is a new breakthrough in the search for a male equivalent of the Pill.

A previous jab, using hormones to disrupt sperm production in the brain, was found to cause side effects including depression and muscle pain, which saw 20 men drop out of a year-long trial.

The new non-hormonal injection has had a 100 per cent success rate in monkeys

But non-hormonal injections, which have a 100 per cent success rate in monkeys, could provide another option for more than 10,000 men a year in England who have vasectomies.

It works by injecting gel into the vas deferens – the tube which transports sperm from the testicles to the urethra – to block it.

As well as being less painful than ‘the snip’, a previous study suggests the gel injection is reversible, saving men who change their mind thousands of pounds for potentially unsuccessful surgery to reverse their vasectomy.

It could be trialled in people as early as next year, after working in 16 male rhesus monkeys which failed to impregnate female monkeys over up to two years.

Professor Adam Balen, chair of the British Fertility Society, said: ‘This is an interesting technique that achieves a reversible “vasectomy” by blocking the passage of sperm with a substance that later can be flushed out.

‘If free of side effects, then this novel approach has the potential for great promise as a male contraceptive. It is essential to know that the reversibility remains, irrespective of the duration of use.’

If trials next year are successful, the breakthrough could lead to a male equivalent of the Pill

Fertility expert Allan Pacey, professor of andrology at the University of Sheffield, said there could be a ‘worldwide market’ for an effective male contraceptive.

He added: ‘The idea of trying to replace the traditional method of vasectomy by inserting a gel into the tube which carries sperm from the testicles to the penis at ejaculation is not a new one.

‘However, we haven’t seem much progress in developing the idea in recent years, so this study is a useful step in the right direction.’

There is a race to find a working male contraceptive, which would take the pressure off women to prevent pregnancy. Scientists have also looked at switching off sperm’s ability to swim and disrupting brain signals to block sperm production.

The use of a gel, called Vasalgel, to prevent sperm from being released within semen, was found last year in a study of rabbits to be effective for 12 months.

It works similarly to a vasectomy, which also blocks or cuts the vas deferens to stop sperm travelling from the testicles to the penis. But, unlike a vasectomy, which most men have to pay to have reversed privately, with a success rate as low as 30 per cent, the gel injection was found in rabbits to be reversible.

The latest study, published in the journal Basic and Clinical Andrology, was done to test if, as well as blocking sperm in rabbits, the injection would prevent pregnancy.

Experts say there is a 'worldwide market' for an effective and long-lasting male contraceptive

A team at California National Primate Research Centre monitored rhesus macaques given Vasalgel for at least one breeding season during which 80 per cent of the females housed with them would normally fall pregnant.

But, over an average time period of almost 1.2 years, and up to two years for some monkeys, there were no pregnancies.

This success rate is better than the Pill, which offers effectiveness of around 99 per cent in people, and uses animals far closer to humans. Clinical trials are due to start in early 2018.

The side effects seen from hormonal injections, which have seen men in human trials reporting mood disorders and pain, were not seen in the monkeys. There was a case of one developing a sperm granuloma, a lump caused by leaking sperm, but this was less likely than following a vasectomy.

Previous research has shown that the majority of men are seeking a male contraceptive but many are concerned about the side effects of hormonal injections.

On the results of using gel, lead veterinarian Angela Colagross-Schouten said: ‘We were impressed that this alternative worked in every single monkey, even though this was our first time trying it.’