Clemens Bimek says his invention, a “gummy-bear” sized switch, involves a simple 30-minute medical procedure placing a valve on each spermatic duct.

So far, the inventor is the only brave soul to have tried the device, which once inserted, is controlled by a switch underneath the scrotum.

However, doctors have warned the process may not be entirely reversible if the ducts are scarred by the valve.

Speaking to the German publication Speigel, Mr Bimek said: “Many of the doctors I consulted didn’t take me seriously. But there were some who encouraged me to go on tinkering and helped me with their expertise.”

Although the valve is set to be trialled in 25 men, experts highlighted potential problems with the procedure.

Urologist, Hartwig Bauer, who has performed the surgery, also told Speigel: “A third of patients want to have the operation reversed later, but it doesn’t always work.”

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