Customs officials have seized six million cigarettes and 4.5 tonnes of rolling tobacco during checks at Rotterdam port. The illegal tobacco products were found a month ago but the haul has only just been made public.

The cigarettes, known as “illicit whites” in official jargon, are considered illegal in the Netherlands because the brand is not officially recognised within the EU. If they and the rolling tobacco had been sold officially, they would have generated €3.9 million in tax income, officials said.

The tobacco was found by sniffer dogs and it is unclear where it originated. The customs statement said that the find had been publicised in the interests of the investigation but did not say if any arrests had been made.

Earlier this year officials seized a consignment of 27 million cigarettes in Rotterdam and last month found eight million illegal cigarettes in a warehouse in Someren in Brabant.

The price of a packet of 20 cigarettes went up by almost a euro earlier this year to around €11.10 as a part of further government moves to discourage smoking.

Yet, while higher taxes on cigarettes are encouraging more people to stop smoking, smuggling is also on the increase, according to research by the finance and health ministries which was published in June.

Once every two years researchers collect empty cigarette packets thrown on the street and check their origins, to gain an insight into smokers’ behaviour in the Netherlands.

In 2021, during the last survey, 15% of the empty packets had contained cigarettes which had not been subject to Dutch tobacco duties. That had risen to 25% last year, the ministries said on Tuesday.

While nearly 19% of the cigarettes had been bought in a shop in another country,  4% were either fake branded cigarettes or had been smuggled in. Two years previously, just 1% were either fake or illegal.

Research by the public health institute RIVM also indicates that smokers buy around 10% of their tobacco abroad, either by importing it themselves or asking others to do so.