A good catch of endangered toothfish far outweighs later fines

But efforts to board the long-line trawler Viarsa, believed to be carrying up to A$5m (US$3.3 m) worth of the rare and valuable fish, have so far been hampered by bad weather, officials said.

A British ship has joined Australian and South African vessels already engaged in the pursuit of the trawler, which was first sighted on 7 August in Australia's fishing zone, 4,000km (2,200 nautical miles) south-west of the mainland.

The Australian patrol boat Southern Supporter gave chase, suspecting the trawler had been fishing illegally.

Twenty days and more than 7,400 km later, it is still chasing.

The skipper of the Viarsa has refused repeated requests to stop, but the Australians have stuck with him, battling through the huge winter seas of the Southern Ocean, at times dodging icebergs.

A week ago, a South African icebreaker joined the chase.

Now the British Fisheries protection ship, the Dorada - normally based in the Falkland Islands - is also closing in.

Uruguay acts

Conditions at the interception point, about 3,000 km south-west of Cape Town, are described as being extremely severe.

The Patagonian Toothfish can command huge prices

All four vessels are said to have encountered snowstorms as well as the full ravages of the Southern Ocean.

But the Uruguayan ship is still reported to be trying to head to South America at full speed.

Uruguay itself has said it will allow Australia to inspect the vessel if it finally reaches port in Montevideo.

Its ambassador to Canberra, Pedro Mo-Amaro, said the Viarsa had ignored Uruguay's advice to head to an appropriate port and had severed all communication.

"If this ship is not apprehended and it arrives in Montevideo, we guarantee we will let the Australian authorities inspect the vessel," Reuters news agency quoted him as saying.