Saudis have been racing to buy Singer sewing machines for up to fifty-thousand dollars because they believe they contain traces of red mercury. This is a substance which may or may not actually exist.

Some sources say it can be used to make a devastating, pure nuclear fusion bomb. Others say it's an urban myth.

In 2006, it featured in the British trial of three men accused of trying to make a dirty bomb. They went looking for red mercury, but during the course of the trial it became clear that no-one - not even the defendants themselves - knew what it was. But that hasn't stopped internet sites suggesting that one kilogram of the substance can fetch hundreds of thousands of dollars on the black market.

However the rumours in Saudi Arabia started, it's the hope of such huge profits that's caused the sewing machine buying frenzy. Saudi papers have pictures of old men with pick-up vans, stacked with piles of sewing machines.

People believe they can use their mobile phones to test if the machines contain red mercury. The Saudi authorities say it's all a hoax and they’ve launched a police investigation.