The Canisteo is the second US vessels to arrive at Hartlepool

The ex-US Naval reserve vessel Canisteo joined the Caloosahatchee at Able UK's Hartlepool yard on Thursday, where they will spend at least the next few months.

A question mark remains over whether the ships will be allowed to stay in the UK.

Able UK, which decommissions oil rigs, has won an �11m contract from the US authorities to decommission the disused vessels and has said the future of the site depended on being allowed to complete the contract.

Both vessels are being thoroughly checked by the Environment Agency.

Legal wrangles

Environmentalists on both sides of the Atlantic have criticised the deal, saying waste should be dealt with at source.

They fear the ageing vessels might not survive the 4,000 mile-plus journey and claim they contained harmful chemicals.

Able UK managing director Peter Stephenson has said the work can be carried out in an environmentally-sound manner.

A High Court injunction prevents any dismantling until a series of legal wrangles have been resolved.

Environment Secretary Margaret Beckett said the first two ships could stay in Hartlepool, but she said they should return to the US when it was safe to do so.

Captain William G Schubert, of the US Maritime Administration, said: "We are encouraged by the decision to allow the first two ships to enter Hartlepool, their original destination, for safe keeping."

A further two vessels are continuing their journey and are expected to arrive before the end of November.

On Wednesday, the Environment Agency approved a modification of a waste management licence to allow the ships to dock in Hartlepool.

Conditions will be imposed which will prevent any breaking up of the US vessels in the UK.

Public inquiry

Discussions are under way with US authorities about sending back the other two ships which are just days behind the first two ships.

Able UK says that if the work is not allowed to go ahead it will cost the firm a bond of more than �3m as well as millions of pounds worth of future business.

Business leaders in the region issued a statement backing Able UK and criticised the way the situation had been handled.

Protesters say the ships contain asbestos, fuel oil and other waste.

They have called for a public inquiry into the government's handling of the affair.

The Environment Agency has sought to play down fears over the ships, saying they are no greater risk than much of the shipping going in and out of UK ports on a daily basis.

Oils and oily ballast water could cause damage to the marine environment. Asbestos is a known carcinogen but is denser than water and non-soluble. PCBs have been called "probable carcinogens" and have been linked with neurological and developmental problems in humans. Mercury, lead, chromium and cadmium are highly toxic metals which accumulate in the body.