British anti-fraud police have foiled a Nigerian mass-marketing fraud operation targeted at UK consumers.

The Serious Organised Crime Agency (Soca) seized fake cheques, postal orders and bank drafts worth more than £8m destined for the UK market. Fake passports were also collected.

Soca, which worked closely with the Nigerian police during the month-long operation, also said thousands of bank accounts being used for fraudulent activity have been identified or closed down and arrests made in Nigeria and the UK.

However, Soca admitted that at the moment it had no way of knowing how much disruption and damage it had been able to make to the criminal networks operating these scams.

"We have no way of knowing how big a dent we will have made so will be working with the Office of Fair Trading (OFT) to continue to monitor this crime," a Soca representative said.

In the UK, the total cost of scams such as those thwarted by Soca, is more than £3.5bn every year, according to the OFT. Mass-marketing frauds comprise scams such as fake lotteries, prize draws and advance fee schemes.

They are usually carried out online but the fraudsters can approach their victims by letter or phone. Increasingly people are also being duped on free internet dating sites.

The consumer watchdog said one in 10 adults had fallen victim to one of these frauds and last year 3.2 million people handed over cash to fraudsters. Individually, the cost to the victims is usually thousands of pounds and once they have been tagged by the fraudsters as a 'sucker' their details are shared with other criminals.

The UK, along with the United States, Nigeria, Netherlands, Spain and Canada, is coordinating efforts to tackle mass marketing fraud, which is a global issue and increasingly run by organised criminal gangs.

Soca said although it had made arrests and seized the fake documents, the current operation was still ongoing. Intelligence gathered in Nigeria and elsewhere is being shared with British law enforcement agencies including the City of London Police and the Metropolitan Police.

Paul Evans, Soca's executive director, said: "Mass-marketing fraud is a low-value, high-volume crime. Relatively small amounts of money quickly add up to big profits for the fraudsters.

"Organised criminals respect no borders and international cooperation is vital when tackling this type of fraud. We are working with partners across the globe to tackle the fraudsters wherever they may be - from Lagos to London and Amsterdam to Alabama.

"We are particularly grateful to the Nigerian authorities whose assistance and commitment has been unrelenting."

Consumers can find information on different types of fraud and advice on how to avoid becoming a victim on the OFT's website or Met police website. Alternatively they can contact Consumer Direct on 08454 04 05 06.