Cheap cigarettes containing twice the level of cancer-causing chemicals are being sold on the streets of London.

Many are being bought by schoolchildren, according to trading standards officers in the borough of Camden, north London.

The fake cigarettes are wrapped in packets of Regal and Silk Cut, carry the British Government's health warning and also look like the real thing.

But laboratory tests have shown they contain high levels of tar, nicotine and banned chemicals.

A tout was secretly filmed by BBC London

Martin Butcher from the Camden Primary Care Trust has been working with Camden Trading Standards to have the tests carried out.

He said there was particular concern that more than half of the borough's 10- to 14-year-olds who smoked, knew where to buy the counterfeit cigarettes.

Mr Butcher told BBC London: "We are particularly concerned because kids are buying these cigarettes.

"They're buying them at the age they can get addicted to smoking.

"These have got a lot more nicotine in and they're a lot more dangerous."

Counterfeit cigarettes

75% more tar 28% more nicotine 36% more carbon monoxide

Another fear, according to a laboratory report, is that the cigarettes could be contaminated with foreign materials, including plastics, wrapping materials and even sand.

Des Campell, head of Camden Trading Standards, said: "These results are shocking. This strengthens our commitment to tackle the problem of smuggled tobacco and the sale of all tobacco to children."

Customs and Excise officials believe that more than 20% of the cigarettes they seize are likely to be counterfeit.

Many of those are produced in workshops in China in unhygienic conditions,

Experts think more than 100 billion counterfeit cigarettes are produced each year in remote villages in China.