The successors to Silk Road, the darknet drug market shut down by the FBI in 2013, are raking in tens of millions of pounds in total revenue every month, according to a new report.

British dealers apparently have a serious finger in the pie, taking home roughly 16 percent of the global revenues, or around £1.75 million, between an estimated 338 vendors.

The report, commissioned by the Dutch government to gauge the growth of darknet markets in the years following the demise of Silk Road, found some good news for beleaguered law enforcement: "cryptomarkets have grown substantially in the past few years, but not explosively," though the numbers of vendors and hosting sites have grown. In fact, researchers found around 50 of these markets in total, however, the total volume of listings is now only six times larger than in 2013.

Among the eight most popular marketplaces surveyed, there are plenty of illicit goods and services to buy, the vast majority (57 percent) of the listings were found to offer drugs. Over a third featured cannabis derivatives (37 per cent), stimulants (29 percent), and members of the ecstasy family (19 percent).

Researchers also found that a quarter of listings were priced above £768 ($1,000), implying that many dealers were using online markets to buy in bulk for offline sale.

The often-used analogy "an eBay for drugs" is not entirely correct, because eBay is intended as an online retail market. This is an important finding. Cryptomarket trade may have an impact beyond creating a new way for drug users to access a wide range of drugs; based on the extent of wholesale transactions, we believe it is likely that many cryptomarket customers are drug dealers sourcing stock intended for offline distribution. Cryptomarkets may therefore be diffusing a wide range of substances into local offline drug markets.

In all, researchers estimate that cryptomarkets generated a total monthly revenue of between £9.2m ($12m) and £16m ($21m) in January 2016, or several million more when the prescription drugs, alcohol, and tobacco which were also found for sale are included.

Most vendors (890) were based in the US, with the UK in second place, followed by Germany with 225 sellers. Intercontinental trade is common, with many vendors willing to ship to Australia and New Zealand, though intracontinental deals are more usual.

The balance of evidence suggests that as security techniques are honed, increasing numbers of buyers and sellers are feeling confident enough to evade detection. In its overview of detection methods, the report admits that as the "Internet-facilitated drugs trade is still a relatively new and continuously evolving phenomenon... strategies may not be fully developed yet."