More than one third of London’s smokers have purchased illegal tobacco, some of which contained asbestos and human excrement, new research has revealed.

Undercover shoppers found one in eight London retailers – including shops in East Ham and Forest Gate – are selling illegal tobacco products.

The highest rates of sales were found in convenience stores where some retailers were selling cigarettes for as little as £3 a pack.

The shocking findings by Japan Tobacco International (JTI) also revealed that many of the “under the counter” cigarettes came with added nasty ingredients such as mould, dust, dead flies and rat droppings.

JTI has raised the concerns ahead of the introduction of plain packaging and restriction on pack sizes of tobacco on May 20 which it says could worsen the illegal tobacco trade in the capital.

This is because it will become easier and cheaper to produce counterfeit cigarette packs which could mislead customers into believing they are buying a genuine product.

Young people will also be at greater risk of being targeted by organised criminal gangs.

Already, 62 per cent of people say they would buy illegal tobacco products to save money.

Steve Wilkins, JTI’s anti-illegal trade operations director and former Det Ch Supt said: “Smokers buying cheap fake cigarettes and tobacco on the streets of the UK may be getting more than they bargain for as these fake imitations has been found to contain asbestos, mould, dust, dead flies, rat droppings and even human excrement.

“The availability of cheap illegal tobacco across towns and cities in the UK is damaging local communities and along with retailers, suppliers and the government we all have a role to play to combat the issue.

“Anyone with information about this type of crime should contact Crimestoppers anonymously on 0800 555 111.”

A HMRC spokesman said: “The UK faces a continued threat from cheap illicit tobacco products.

“The majority of retailers are law-abiding traders. However, there are those who believe they can make easy money by selling illicit tobacco products under the counter.

“HMRC continues to develop and refine the methods used to combat the ever-changing nature of illicit trade.”