At Cardiff Crown Court, Mr Justice Steel said a "substantial" fine was needed to "reflect the genuine and justified public concern" in an incident estimated to have cost pounds 56m in lost tourist and fishing revenues and a further pounds 60m in clean-up expenses.
The 147,000-tonne Norwegian tanker ran aground in February 1996 when an inexperienced pilot, John Pearn, tried to take her into the Port of Milford Haven at low tide.
She lay wallowing on rocks for nearly a week before being salvaged, and let loose a flood of 72,000 tonnes of North Sea crude oil.
It damaged beaches along a 120-mile stretch of some of the most protected coastline in Britain, much of it in the Pembrokeshire Coast National Park. About 25,000 seabirds are thought to have died, including large numbers of common scoter ducks, guillemots and razorbills. Shellfish beds were laid waste and have still not recovered.
In a prosecution brought by the Environment Agency under the Water Resources Act, Milford Haven Port Authority pleaded guilty to an offence of causing pollution in controlled waters, and in addition to the pounds 4m fine was ordered to pay the Environment Agency's legal costs of pounds 825,000.
Milford Haven's harbour master, Captain Mark Andrews, had his pleas of not guilty accepted earlier this week when he denied three charges relating to the tanker's grounding.
The fine and costs more than quadrupled the previous highest pollution penalty of a pounds 1m fine for Shell.
Oil from its Stanlow refinery near Ellesmere Port spilt into the River Mersey in 1989. In another case, British Steel was fined pounds 200,000 with costs of pounds 101,000 in 1991 after diesel oil leaked into the Severn estuary.
But many recent pollution fines have been trivial compared with the financial resources of the companies or organisations found responsible. The Environment Agency's chief executive, Ed Gallagher, who has often called for higher fines, said he was pleased with yesterday's result, which he said was an important landmark in environmental protection. "The extent of the financial consequences of this incident will cause all those involved in oil production and transportation to review their procedures seriously," he said. "It will also cause those businessmen who cynically calculate that a bit of environmental damage and the usual low fine are a cheaper and more acceptable alternative to operating their equipment and factories properly, to think again."
The Sea Empress ran aground on the evening of 15 February on rocks at St Ann's Head at the entrance to the Milford Haven waterway, because, the judge said, of the "careless" navigation of Mr Pearn, who had never before attempted to take a vessel of similar size into the harbour close to low tide.
Although the pilot, an employee of the authority, was not prosecuted, the judge said it was necessary to identify the errors so as to put the port's position in context.
"The pilot was put in a position by the port authority where he could make an error of navigation," the judge said. Milford Haven Port Authority has since reviewed its grading, training and examination of pilots.
After the case, however, the authority warned that the huge fine could have implications for the viability of the business, which employs 200 people in Pembrokeshire.
Ted Sangster, general manager, said an appeal against the severity of the fine would be considered.
"This level of costs will greatly impair the future of the business," he said.Reuse content