At next month's International Whaling Commission meeting in Grenada in the West Indies, the Japanese will formally propose scrapping the sanctuary, eight million square miles of ocean around Antarctica that is home to some 90 per cent of the world's remaining biggest whales. Britain will "vehemently" oppose the move, the Fisheries minister, Elliot Morley, said yesterday.
The Japanese have disregarded the sanctuary since it was established in 1994, continuing to hunt whales in its waters for what they call "scientific" purposes, as they have done since the current world moratorium on commercial whaling came into force in 1986.
Their attempt to scrap the sanctuary is part of the pressure Japan and the other principal whaling nation, Norway, are applying to have the moratorium lifted. To the alarm of anti-whaling campaigners worldwide, this is beginning to look as if it might succeed.
To abolish the sanctuary the Japanese will need a three- quarters majority of those countries voting at the IWC meeting, and they can already count on the support of a number of small states that have voted with them in the past after receiving substantial Japanese aid.
But they will be forcefully opposed by the anti-whaling countries led by the US, Australia, New Zealand and Britain.
"The Japanese have never liked the sanctuary and we are not surprised they want to see it abolished, but we will vehemently oppose any attempts by them to do so," Mr Morley commented.
"They have client states in the West Indies and they are also certainly twisting their arms for support, but we have powerful allies."
Mr Morley reaffirmed that Britain remains opposed to whaling in principle. And he castigated Japan for continuing its "scientific" whaling programme, under which hundreds of minke whales are hunted and killed every year, and their meat sold commercially in the name of "research".
"We oppose this and strongly criticise the Japanese for it," he said. "I wish Japan would listen to world opinion a bit more and take a more reasonable position. They have not been reasonable.
"Whaling is not a very important part of their economy and there is not that big a demand for whale meat, certainly not in any way to justify the levels of whaling that have been seen."
Environmental campaigners are equally critical. "Since the creation of the Southern Ocean sanctuary in 1994, Japan has killed some 1,600 whales there, using a legal loophole to disguise its commercial slaughter in so-called scientific whaling," said Sue Fisher of the Whales and Dolphin Conservation Society.
"We hope Britain will take a lead in opposing their attempt to abolish it, and send a minister to the meeting to show its commitment," she said.
In a countermove, Britain is backing proposals by Australia and New Zealand for a new whale sanctuary to be set up in the South Pacific, and by Brazil for one in the South Atlantic.
The current Southern Ocean sanctuary, when added to the Indian Ocean sanctuary set up in 1979, outlaws whaling permanently in one-third of the world's oceans.
The Southern Ocean is the richest feeding ground for whales, and saw killing on such a scale throughout most of this century that the population of some species was driven to the brink of extinction.
The blue whale, the world's largest animal, was reduced in numbers from 250,000 to a few hundred. The next biggest, the fin whale, which was the mainstay of the Antarctic whaling industry, was reduced from half a million to a few thousand. Only the population of the minke whale remains substantial, at an estimated three- quarters of a million.
The point of the sanctuaries is to make whaling off-limits within them even if the moratorium is eventually lifted. A compromise proposal from Ireland, which would allow commercial whaling once more in return for the whaling nations agreeing to tight regulation, will be discussed at the IWC meeting although it will not come to a vote this year.
Anti-whaling campaigners are strongly against the proposal as they say regulation can never be properly enforced.