BBC Correspondent Wyre Davies: One of the biggest oil spills in British maritime history

The authority pleaded guilty at Cardiff Crown Court to one count of allowing oil to pollute large areas of the coastline.

Around 72,000 tonnes of crude oil poured into the sea off the coast of west Wales in February 1996 when the tanker ran on to rocks at the mouth of the Milford Haven estuary.

The authority now faces an unlimited fine under the legislation.

But the prosecution accepted the authority's not guilty pleas to charges of allowing an insufficiently trained and qualified pilot to be aboard the Sea Empress and thereby posing a danger to public safety.

Michael Hill QC, for the Environment Agency, said the prosecution agreed that it would not serve the public interest to pursue the port authority on these charges as the main interest lay in the pollution offence.

BBC Correspondent Wyre Davies reports from Cardiff Crown Court

Mr Hill added the port authority's decision to plead guilty to causing pollution was sufficient to establish its criminal liability in the incident.

The judge also accepted harbour master Captain Mark Andrews's not guilty pleas to three counts of causing pollution and also failing to safely control shipping at Milford Haven.

Pilot took the wrong course

The court was told the ship's pilot who grounded the giant Sea Empress tanker on rocks at low tide had never before attempted to handle a similar vessel on his own.

Pilot John Pearn, 35, had never been trained on a simulator to take a ship like the 147,000-tonne Sea Empress into the entrance of Milford Haven estuary.

He took the wrong course as he approached the mouth of the waterway. Radar installations near St Anne's Head were due to be replaced and were not operating on 15 February 1996, when the Sea Empress ran aground.

A new rule now stipulates that tankers of more than 65,000 tonnes should have two pilots aboard. This had formerly applied to vessels of 150,000 tonnes and over.

The prosecution was brought by the Environment Agency which said the disaster endangered marine life and human health.