This sounds - painful- ?

From vasectomies to the male contraceptive pill, there have been many attempts to shift the burden of birth control burden onto men.

Now one German entrepreneur believes he has the solution - a 'switch' to stop sperm from reaching the penis.

The valve - which is implanted internally - is designed to divert the flow of sperm back to the man's testicles, making him temporarily infertile.

If he later decides he wants a wants to become a father, he simply locates the implant in his scrotum and flicks the switch back, allowing sperm to be ejaculated.

The 1.8cm device is inserted in the scrotum with the recipient able to turn the device on and off to control whether sperm is ejaculated

Clemens Bimek, the inventor, claims the spermatic duct valve has the potential to 'change the world' by offering a contraceptive that is as effective as a vasectomy - without being permanent.

Mr Bimek, a joiner who lives in Berlin, had been watching a documentary on contraception when he had the brainwave.

He is so far the only recipient of the device - which he hopes to fund through €5 million of investment including crowdfunding - with a trial involving 25 men set to start early this year.

The implant - which is 1.8cm long and weighs 2 grams - takes about half an hour to be surgically inserted while the patient is under local anaesthetic.

The valve is implanted in the spermatic ducts with a rocker switch - which can be located easily by hand through the thin skin of the scrotum - and turned on and off.

The switch direction is simple to remember; to open the valve push the switch down towards the abdomen, from where the sperm cells would normally flow.

Once in place, the device, named the Bimek SLV, will continue to work indefinitely, its makers claim.

According to the device's website, in its closed state the valve prevents sperm cells from leaving the testicles and mixing with the semen before ejaculate.

Like a vasectomy, the sperm is instead reabsorbed into the body.

The main difference is that the spermatic duct valve can be opened by the wearer at any time so the fertility is restored, whereas vasectomies cannot always be reversed.