The UK's Food Standards Agency has stepped up its health warning about counterfeit vodka contaminated with methanol in the country after another illegal product was been found on sale.

Customs and Excise officers seized four cases of S. Petersbourg Vodka from off-licences in the Holloway area of Islington, north London, late in June. More than a dozen bottles of the same vodka were seized from off-licences in the Waltham Forest area of north London in an earlier raid.

Laboratory tests on these bottles showed that they contained unacceptably high levels of methanol. "Vodka should not contain methanol at such levels. If consumed it could cause serious harm to health," said the FSA in a statement.

Some bottles found in Waltham Forest were labelled as St. Petersburg Vodka in a slight variation on the spelling of the name. They were also found to contain unacceptable levels of methanol. The FSA said that anyone who may have a bottle of this vodka should not drink it and should contact their local authority.

This latest advice follows a series of warnings from the Agency about the hazards of drinking these fake products. A 42-year-old woman died in March in Edinburgh, Scotland, after drinking counterfeit vodka. The effects of methanol poisoning include abdominal pain, drowsiness and dizziness, blurred vision blindness and breathing difficulties leading to coma. Symptoms can be delayed for several hours and anyone who thinks they may have drunk one of these products should seek immediate medical advice.

The counterfeits have taken the name of a genuine brand of vodka called St. Petersburg Vodka. The product, which was produced in Russia and bottled exclusively for the USA export market, has not been sold for four years. The genuine product is marked 40% strength.