The rusting hulks contain about 350 tonnes of toxic chemicals, 620 tonnes of asbestos and 470 tonnes of old fuel oil and represent a major pollution risk, the Basel Action Network (BAN), a network of groups including Greenpeace and Friends of the Earth, said.

"We have a situation where their condition plus the pollutant load means floating time bombs are heading Europe's way," James Puckett of BAN told journalists.

The first two ships left Chesapeake Bay on the US east coast two weeks ago and are being hauled in tandem by tugboats to northeastern Britain, crossing the English Channel and French and Belgian territorial waters on their way, Puckett added.

They are due to arrive in Teesside on November 5, where they are likely to be dismantled by a local shipyard while lying in a river estuary, increasing the risk of pollution, according to BAN.

"The permits to construct a dry dock do not yet exist," Puckett said.

BAN said Washington's decision this month to reverse the previous US administration's freeze on scrapping vessels abroad highlighted the need for ships to be included in an international agreement which regulates the export of industrial waste.

Concerns about pollution from shipping are riding high in Europe, and single-hull tankers carrying heavy fuel oil were banned from European Union ports under new rules adopted on Tuesday.

There are nine more ships ready to be sent to Britain and 150 old vessels from the US ghost fleet are slated for scrapping abroad, BAN claimed.

Experts resumed talks on expanding the 1989 Basel Convention on transboundary waste in Geneva this week, and have started dealing with the issue of dismantling old ships and the toxic chemicals they might contain such as PCBs (Polychlorinated Biphenyls).

The convention, signed by 158 countries, but not the United States, partly outlawed the export of hazardous waste from industrialised to developing countries and regulated other movements, after "toxic traders" began dumping industrial waste in eastern Europe and poor countries in the 1970s.

Greenpeace believes the ship-breaking trade is following largely the same trend. It wants hazardous materials removed in the countries of origin before the vessels are beached and dismantled by an army of cheap labour in developing countries.

"Along with other organisations in India and Bangladesh we are trying hard to stop the ongoing pollution which is associated with the breaking of these ships," Frank Petersen of Greenpeace International said.

"We are calling on the Basel Convention to get its act together," he added.

Some 450 ships have been sent for breaking in various countries in the world so far this year, Greenpeace said.