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Mephedrone, or miaow miaow, was made illegal in 2010.

The ONS figures covering England and Wales also showed a significant rise in the number of people killed after inhaling helium.

There were 58 deaths involving the gas last year, up from 12 in 2008, and many were linked with suicides, according to the ONS report.

In all, 891 women died from drug poisoning - including legal and illegal drugs - which was a rise of 880 the previous year.

In the same period the number of male deaths fell 4 per cent to 1,706.

The number of deaths involving heroin or morphine fell slightly in 2012 to 579 deaths, but these remained the substances most commonly involved in drug poisoning deaths, the ONS said.

The 30 to 39 age group saw the most deaths from drug misuse, and the North West had highest mortality rate by area.