Counterfeit cigarettes containing up to 500% higher levels of cancer-causing chemicals are undermining efforts to reduce smoking, councils have warned.
Available on the blackmarket, the fake cigarettes are often cheaper than their genuine brand-name counterparts, but many contain far higher levels of toxic ingredients such as tar, nicotine, carbon monoxide, lead and arsenic, according to the Local Government Association (LGA).
They may also contained up to 500% more of the toxic metal cadmium.
The LGA, which represents more than 370 councils, also warned that fake cigarettes pose a greater fire risk as they do not include components that ensure they self-extinguish if not actively smoked.
Manchester, Croydon and Coventry have recently seen raids and prosecutions by councils, with trading standards officers finding illegal stashes hidden under floorboards, in toilet cisterns, in boxes of sweets, behind extractor fans and ceiling lights, and beneath a motorised lift.
Simon Blackburn, chairman of the LGA's Safer and Stronger Communities Board, said the millions of fake cigarettes were "funding organised criminal gangs, damaging legitimate traders and robbing the taxpayer of more than £2 billion".
A Department of Health spokesman said: "Smoking is the biggest preventable killer in our country. Illegal cigarettes are extremely dangerous - even more so than normal cigarettes because they are not checked and could contain anything."
Consumers concerned about any tobacco product on sale can report the matter to the Citizens Advice consumer helpline on 08454 04 05 06.