South Korea’s Prime Minister and his entire cabinet offered to resign this morning as riot police across Seoul prepared the centre of the city for a night of mass demonstrations and violence.

Korean police – well used to the country’s often explosive political protests – raised their state of alert to the highest possible state as public feeling over the “mad cow” crisis threatened to spiral out of control.

The demonstration is timed to coincide with the 21st anniversary huge pro-democracy protests that shook the authoritarian regime of the time to its foundations and paved the way for the country’s first free elections.

Tuesday’s resignations follow more than a month of widespread protests throughout South Korea over government plans to re-start imports of American beef, which were suspended five years ago amid concerns over BSE. Washington has repeatedly asserted that its beef is safe, but ordinary Koreans remain deeply skeptical.

Barricades made from giant steel containers have been thrown up around the main squares in the centre of Seoul amid predictions that as many as 300,000 anti-US beef demonstrators would clash with both riot police and large numbers of pro-government conservatives. 20,000 armed police have reportedly been called-up to bring order to the streets.

Both the resignations and the expected trouble on the streets plunge the three-month old presidency of Lee Myung Bak into deep crisis. Since February, Mr Lee has weathered a breakdown in relations with North Korea, a scandal that claimed the patriarch of Korea’s most famous company, and an inflation menace that now threatens to derail the economy.

But the mass hysteria over the supposed dangers of US beef imports has proved the most damaging. Despite sweeping to power in February in a record landslide electoral victory, the conservative, pro-business leader has seen his popularity fall further and faster than any of his predecessors.

The resignation offered by Prime Minister Han Seung-Soo and his ministers provides the demonstrators with some impressive scalps, but political analysts said it was not clear that they would be enough to dilute anti-government feeling. The “mad cow” protests mask a surprisingly strong mistrust of Mr Lee, despite his overwhelming victory at the polls.

The country’s hyperactive online community has whipped-up concern over BSE, and demonstration organisers believe that more than a million people will take to the nation’s streets tonight. At the height of the “mad cow” mania, demonstration organisers have suggested – with no scientific backing - that plans to re-start US beef imports were tantamount to a death sentence on young Koreans.

The hysteria was especially potent among university and high-school students, many of whom have gone straight from their classrooms to join demonstrations each evening. To the government’s extreme consternation, many teachers have given their tacit backing to their students’ behavior.

The vehemence of recent protests last month was enough to delay Mr Lee’s plans to begin US beef imports, which are now being tweaked to make them appear more acceptable. The re-starting of beef imports is part of a wider free trade agreement struck between Seoul and Washington in the last days of Mr Lee’s now widely despised predecessor, Roh Moo Hyun.

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