The legal high drug mephedrone will be banned within weeks, Alan Johnson, the home secretary, announced today.

Emergency legislation classifying mephedrone as a class B drug comes after Johnson's expert drug advisers disclosed that the drug has been implicated in 25 deaths in England and Scotland.

The ban is expected to gain cross-party support to be rushed through both houses of parliament in the four remaining sitting days before the general election.

The decision to push ahead with legislation comes despite the resignation of a further member of the government's Advisory Council on the Misuse of Drugs, which left a legal question mark.

Johnson has brushed aside the effects of the latest resignation, that of Dr Polly Taylor, a consultant veterinary surgeon, whose decision to quit leaves the ACMD inquorate and technically unable to make a recommendation to the home secretary. Home Office lawyers are confident that the ban can go ahead. Taylor's term on the council was due to end shortly and candidates have already been interviewed for her place.

The decision to classify mephedrone as a class B drug alongside the amphetamines it imitates will also extend to other cathinones which have been synthesised by south-east Asian chemists from the active ingredient in the plant qat.

Professor Les Iversen, who chairs the ACMD, said that the rise in popularity of mephedrone – also known as meow meow or drone – was unprecedented: "I have never experienced such a widespread use in such a short space of time. There is no question this is the drug of the moment," he told the ACMD meeting today in London.

"It is being taken by young people who have never taken drugs before in their lives because they think it is legal and it is safe. It is neither legal nor safe."

He said the figure of 18 possible mephedrone-related deaths in England was based on data from the National Programme on Substance Abuse Deaths, which collates information from police forces and forensic labs. Iversen said they were regarded as the most reliable source but cautioned he was only saying the drug was possibly implicated in those deaths. Full postmortems have yet to be carried out. A further seven cases have been reported in Scotland, although only one so far has been confirmed as a mephedrone-related death and the heroin substitute methadone was also reported to be a factor in the case.