By Danny Wood BBC correspondent in Madrid

An estimated 25,000 tons of oil from the shipwrecked tanker Prestige have polluted the coast of Spain, Portugal and France.

The government of the Spanish region of Galicia, the French authorities, the Bahamas - where the Prestige was registered - and the ship's insurer, London Club, are all conducting separate investigations into why the vessel sank.

The investigation by Galicia's government is in chaos.

Opposition parties walked out of proceedings after Spain's Prime Minister, Jose Maria Aznar, refused to allow national authorities and officials to appear before it.

Bottom of the ocean

Paul Hinton, Chief Executive of London Club, the insurer of the Prestige, says their investigation is being made difficult by a number of hurdles:

• A lack of cooperation from the Spanish authorities
• Important documents are at the bottom of the ocean
• Insufficient access to the ship's captain, Apostolus Magouras, who remains in Spanish custody

The main investigation is by the Bahamas Maritime Authority, who registered the Prestige.

Bad weather is hampering the clean-up

Deputy Director Steve Clinch says they have virtually ruled out a container or a large wave as the cause of the breach in the ship's hull.

They are looking closely at the practice of steel replacement in old vessels and repair work done on the Prestige in China in May 2001.

The hole in the hull occurred where old steel had been replaced with new.

The Bahamas Maritime Authority say it is likely they will release an interim report in the coming weeks.