LONDON The sale of some cold remedies will be restricted to one small pack per customer to prevent gangs making the crack-like drug, crystal meth.
Government medical advisors said on Wednesday that large packs of decongestants containing the chemicals ephedrine and pseudoephedrine would be withdrawn from sale.
They would be replaced by packs of 12 or 24 tablets containing a total of 720 mg of the drugs.
The move follows police concerns that criminals are using the ingredients to manufacture methylamphetamine -- crystal meth -- in illegal laboratories.
Although use of the drug is low in Britain, the government is anxious to prevent the problem growing to the serious levels seen elsewhere.
However, the medicines will remain on sale at pharmacies and not become prescription-only, as had been suggested in a consultation which ended in June.
Drugs manufacturers, who had lobbied against prescription-only sales, welcomed the new restrictions.
"This is a sensible and proportionate approach to a problem that is still almost non-existent in this country, but one we all want to avoid," said Sheila Kelly, executive director of the Proprietary Association of Great Britain (PAGB).
There has been only one known case -- on the Isle of Wight -- of an illegal crystal meth lab in Britain using pharmacy products, the PAGB says.
The restriction will affect around one in 10 cold remedies sold in Britain, including versions of Actifed, Benylin, Lemsip, Meltus and Sudafed.
All are already only sold in chemists and are kept behind the counter.
The smaller pack sizes would be sufficient for around three days' treatment, the PAGB said.
Most people only need to take decongestants for one or two days, it added.
A government advisory body will monitor the restrictions for the next two years to check they are working.
It will retain the option to recommend moving the medicines to prescription sale if the measures do not reduce the risk of illegal crystal meth manufacture.