A hundred litres of illegal booze and thousands of cigarettes were seized in raids by officers from HM Revenue and Customs.
Officers, joined by staff from Harrow Borough Council, visited off-licences and convenience stores on Wednesday.
They seized 16kg of hand rolling tobacco, 7,000 cigarettes and 100l of wines and spirits, on which a total of £6,000 of tax duty had not been paid.
Jennie Kendall spokesperson for HMRC, said: “This illegal trade has a devastating impact on legitimate retailers, who have to compete with black market traders.
“It’s robbing the UK economy of vital funding and those selling these goods do not promote they are buying them from criminals - the profits of which are funding organised crime to the detriment of all our communities.”
She also appealed to members of the public to contact customs if they have information on businesses with illegally imported goods.