Italian scientists say they have proved Napoleon was not poisoned, scotching the legend the French emperor was murdered by his British jailors.

Napoleon's post-mortem said he died of stomach cancer aged 51, but the theory he was assassinated to prevent any return to power has gained credence in recent decades as some studies indicated his body contained a high level of the poison arsenic.

"It was not arsenic poisoning that killed Napoleon at Saint Helena," said researchers at the National Institute of Nuclear Physics and the University of Pavia who tested the theory the British killed him while he was in exile on the South Atlantic island in 1821.