A drop in the purity of cocaine has increased fears over its safety
Drug advisers are to review the effects of cocaine, amid concerns youngsters increasingly take it in the mistaken belief it is "relatively safe".
The Advisory Council on the Misuse of Drugs says the five-fold increase in the proportion of users since 1996 is "deeply concerning".
Its head, Prof Les Iversen, told Home Secretary Alan Johnson the drug should remain Class A and was "very harmful".
He took over as chairman after Mr Johnson sacked Professor David Nutt.
The cocaine review is one of the council's first new undertakings since Prof Iversen took over as chairman.
His letter quotes the latest British Crime Survey statistics which suggest 6.6% of 16 to 24-year-olds use cocaine, in comparison with 1.3% in 1996.
Use among those aged 16 to 59 increased from 0.6% to 3% during the same period.
"Cocaine is a very harmful drug to individuals and more broadly society, and evidence of the continued increasing prevalence of cocaine use is deeply concerning," Professor Iversen wrote.
The average purity of seized cocaine had been steadily falling to 15.5% between April and June 2009, he said.
This had "possible implications for harms to users due to an increase in the volume of cutting agents which may be present in a sample".
On Monday, a National Treatment Agency for Substance Misuse report suggested some 3,000 people aged 18 to 24 sought treatment for cocaine addiction last year - a third of all those in England. Another 745 users were under the age of 18.
Professor Iversen added that it was an "increasingly common misapprehension that cocaine is a relatively safe drug".
Recovered cocaine addict Tom Kirkwood, chief executive of addict help service TTP Counselling, said the drug was being used across society.
"From guys who work on construction sites, dinner parties to folks down the pub," he said.
He said it had been "far, far too easily available", and added that policing of cocaine supply had been weak.
On Wednesday, the Commons Home Affairs Committee is expected to criticise law enforcement agencies for not doing enough to stop the supply of cocaine into Britain.
The advisory council's cocaine review is expected to take about a year and will begin after it reports on "legal highs" such as mephedrone, which have been causing increasing concern.
The home secretary said he had to remove Professor Nutt because he had been "lobbying" to change government policy after ministers reclassified cannabis as Class B against his advice.
Professor Nutt has since set up a rival panel, with four other former advisory council members who resigned in protest at his sacking.