A German carpenter has invented a valve which he claims will revolutionise contraception, by allowing a man to turn the flow of sperm from his testicles on and off at the flick of a switch.

Clemens Bimek told Spiegel magazine the idea first came to him some 20 years ago, when he was watching a television documentary about contraception, and wondered whether it would be possible to control the flow of sperm with a simple valve.

He then filed a patent for the device.

So far he is the only person that has had the implant.

There are currently 20 volunteers waiting to undergo the procedure.

The final verdict on the efficacy of the procedure is unknown.