It has become an offence to possess the so-called "date rape" drug Rohypnol without a prescription for its use.

Women's groups on both sides of the Atlantic say the drug has been used by rapists to leave a victim powerless to stop an attack.

The BBC's Andrew Burroughs says the drug is 10 times more powerful than other sedatives (41")

It can also leave victims with confused memories for days after an attack, by which time the drug will have disappeared from the blood and there will be no forensic evidence of a rape.

The US Government says it is responding to the fears by rescheduling the drug under tighter legislation.

Rohypnol, manufactured by Hoffman La Roche, is odourless and tasteless if added to alcohol.

Hoffman La Roche is adding a special blue dye to the drug, which is only released if it is put in alcohol.

The drug is odourless and tasteless in alcohol

The drug is 10 times stronger than other sedatives and its use by rapists first came to light in the USA.

British campaigners against the drug says there is evidence it has been used in the UK but police say they have never found proof.

However, the Department of Health and the Home Office say that anyone caught breaking the new rules faces up to two years in jail, an unlimited fine or both.

Popular with clubbers

Rohypnol, the brand name for flunitrazepam, is prescribed privately in Britain for back pain and insomnia.

It is readily available for just £1 a tablet and has gained popularity among night clubbers who use it to come down after taking ecstasy or amphetamines.