Lethal chemical can be bought on the internet for a few pounds

Osmium Tetroxide is lethal and can be bought on the internet for less than £17 a gram, but experts say it is not as dangerous as the sarin gas unleashed on the Tokyo subway in 1995 which killed 12 and injured 6,000.

Osmium Tetroxide is lethal and can be bought on the internet for less than £17 a gram, but experts say it is not as dangerous as the sarin gas unleashed on the Tokyo subway in 1995 which killed 12 and injured 6,000.

Companies selling the compound warn it is "extremely hazardous" but offer it for sale in glass containers that can be stored in a refrigerator.

Tiny concentrations of its fumes in the air are highly toxic and can lead to death. The poisonous cocktail is a by-product of osmium, one of the heaviest metals known to man. Its name comes from the Greek for "stench" and reflects its odour. Osmium occurs in platinum and nickel ore and alloys of it have been used in ballpoint pens, record player needles and pacemakers. But when osmium is exposed to air, the highly toxic oxide ­ osmium tetroxide ­ is produced.

The liquid is used as a staining agent in detecting fingerprints and to stain objects being looked at under microscopes.

A US firm offers to deliver osmium tetroxide in solid form for $30 a gram (£16.35) or $180 (£102) for 10ml in liquid form.

Alastair Hay, professor of environmental toxicology at Leeds University, said: "You can get hold of small quantities but in a bomb they would be diluted in the air and less of a problem than the blast. If you have significant amounts, it would be different."