It seems a diplomatic given that China does not want North Korea to collapse. There was a time when this was undoubtedly true. However, there are now strong grounds for believing this analysis is wrong.

North Korea has become a liability to its Chinese ally. It only survives on Chinese credits for the oil and food that Beijing dispatches to keep the country’s addled economy afloat. Its one-million-strong army is as much a threat to China as it is to South Korea. The prospect of a nuclear-armed Pyongyang has very probably convinced the Chinese that it is time to put a halt to the dangerously unpredictable Kim Jong Il regime.

Closing down North Korea would be a win-win situation for the Chinese. It would stop in its tracks any thought the Japanese had of going nuclear themselves and thus preserve the balance of power in China’s favor. It would also sharply diminish US influence in the region.

A united Korea would have no further need of US protection, not least its so-called nuclear umbrella. The Americans would almost certainly have to quit their bases. There would be no question of US troops moving up to China’s border.

Seoul and Beijing have been enjoying excellent relations recently. A reunified Korea would pose massive short-term economic challenges, undoubtedly far greater than those encountered when Germany reunited in 1990. However, ultimately, China would have a vibrant market of over 70 million people on its doorstep and a thrusting and reliable trading partner and ally.

There are thought to be at least 100,000 North Korean refugees (one estimate has a quarter of a million) who have fled to China. These people would return home, many taking with them an important appreciation of Chinese culture and society.

The biggest boost to China from reuniting the Koreas would be that such a demonstration of its power and influence would radically boost its international standing. Possibly Beijing has deliberately allowed the situation with Pyongyang to reach this pitch before it has intervened decisively.

The discussions yesterday between Kim and the Chinese envoy Tang Jiaxuan were clearly uncomfortable for the North Korean ruler. The North Koreans have promised there will be no more nuclear tests. This diplomatic triumph earns Beijing international gratitude. It pulled off the coup not by US-style cowboy bluster and chest-thumping but by quiet and obviously tough negotiation.

But is it likely that Chinas intervention is going to stop at this? During the discussions, were the first hints perhaps dropped that Kim and his lieutenants might enjoy extremely comfortable retirements in China if they abandoned power?

Maybe not. But Beijing has flexed its muscles decisively and demonstrated how utterly reliant Pyongyang is on its support. Will the Chinese now be content to let this reclusive dictatorship continue or is this the first careful move in a strategy to bring about its ultimate downfall?