A diplomatic row has erupted between Spain and Britain over responsibility for the stricken tanker now threatening the north-west Spanish coast with an oil slick.

Fears are growing that the Greek-managed Prestige could break up in heavy seas, spilling thousands of tonnes of oil into the sea and causing an environmental catastrophe.

In Gibraltar we see yet another case of tax evasion, smuggling and inappropriate behaviour

Loyola de Palacio Spanish EU commissioner for transport

The slick has begun washing up on the picturesque Galicia shore covering birds with oil as salvage teams working from tugs battle to hold the ageing tanker together.

Britain has officially denied Spanish reports that the Prestige was heading for the British colony of Gibraltar when it ruptured on Wednesday night.

UK ambassador Peter Torry in Madrid dismissed suggestions that the tanker's final destination was Gibraltar as "complete nonsense" and said it was heading for Singapore.

Miles of coastline are under threat

On Saturday, the Spanish Development Ministry released documents to show the Prestige loaded up in the Baltic Sea near the Latvian port of Ventspils earlier in November and had Gibraltar listed as its destination.

The EU's Spanish transport commissioner, Loyola de Palacio, rounded on the British colony which Madrid claims for its own.

"In Gibraltar we see yet another case of tax evasion, smuggling and inappropriate behaviour," she told El Pais newspaper.

Meanwhile, local officials in Galicia have accused the captain of the Prestige, Apostolos Maguras, of failing to cooperate in the salvage operation.

A spokesman for the tanker's Greek managers told Reuters news agency that it was a single-hulled vessel - a class of tankers the EU plans to ban from its waters completely by 2015.

Kursk experience

Teams from Dutch salvage company SMIT equipped with floating barriers and pumping systems are battling against atrocious weather to preserve the vessel, about 100 kilometres (65 miles) off the coast.

The Prestige

Registered in the Bahamas, managed by a Greek firm Built in Japan in 1976 Spain says it was cited twice in 1999 for violating safety regulations and was last inspected the same year

They have been using tugboats in a bid to tow the Prestige further out to sea, to prevent more damage.

Winds reaching 80 km/h and seven-metre swells have also prevented rescuers from patching a crack in the hull below the waterline or transferring the cargo to another ship.

The tanker has already leaked out 1,500 tonnes of oil through a 35-metre gash in its side.

A company spokesman, Lars Walder, told Reuters that even if the tanker did sink there was a possibility that its tanks would hold and it "take the fuel with it to the bottom of the sea".

Vital sea life

Spain has imposed a fishing ban along a 100-kilometre stretch of sea between Cape Tourinan and Caion since the appearance of oil on the shore between the cape and Roncudo.

The World Wide Fund for Nature (WWF) warns that if all 77,000 tonnes of the Prestige's is lost the spill will be twice the size of the catastrophic Exxon Valdez spill off Alaska.

Ecologists say corals, sponges and fish will be damaged by the pollution. Migratory birds which stop over in the area are also at risk.

Raul Garcia of the WWF's marine programme said that more than 60% of the local Spanish population depended on fishing for their livelihood.

"If this oil does leak out into the sea, it will devastate marine life and consequently have a tremendous impact on the people in the region," he said.