A big drinker, Mr Kim has seldom been seen rolling drunk in Macau. Fond of the odd spell at a slot machine, he is not known as a degenerate gambler. His generous belly attests to his love of food. Aware of the physical toll of his night-owl existence, sources who know Mr Kim say he takes to the sauna for hours at a time. With his designer label clutch bags, fashionable glasses and leisure suits, he could pass for one of the increasing numbers of mainland high-rollers now thronging Macau’s high-end hotels.

Two or three times a week, Mr Kim will emerge from his hotel suite to feast at restaurants, usually on Korean food. A creature of habit, he is a known regular at several eateries on the newly built Outer Harbour reclamation and on Taipa. Similarly, he keeps to the same late-night drinking haunts, so far avoiding the newer gin palaces now springing up as part of Macau’s US-led casino boom and being led by such glitzy establishments as the Sands, Wynn or Galaxy casinos.

Such pleasures as a late-night street-side drink with friends would be unthinkable in Pyongyang.

Mr Kim is rarely seen with his family, who live quietly in a spacious villa tucked away in a wooded part of Coloane, Macau’s outer island.

For his own accommodation he has a preference for the Mandarin Oriental near the Macau ferry terminal. The hotel is partly owned by Macau’s original casino mogul Stanley Ho Hung-sun, a tycoon known to have his own ties to Pyongyang, having previously attempted casino ventures in North Korea. Mr Kim has also lived for spells in other Macau hotels, particularly when he fears the scrutiny of the outside world.

Whenever he returns from his frequent trips to Beijing, Bangkok, Moscow and Europe, Mr Kim always seems to celebrate his return in style. ‘That’s when he parties the hardest,’ said one source. ‘He likes the company of old friends.’

He is apparently satisfied with the lifestyle he has forged over the past three years, using Macau as a base for his frequent foreign forays. Other members of family less close to him remain in Beijing.

But while Mr Kim continues to enjoy the pleasures of a relaxed Macau existence, western and Asian diplomats now eagerly tracing his movements believe it may be a lifestyle that cannot be sustained.

The economic and diplomatic squeeze on Pyongyang is intensifying after its first nuclear test last October. Even before the incident, Macau’s three-decade links to North Korea were under pressure. Some US$24 million in North Korean accounts at Macau’s Banco Delta Asia remain frozen, with the bank in receivership.

Mr Kim’s continued presence in Macau, while entirely legal, may prove an embarrassment, particularly as the Macau government attempts to show it is no longer willing to act as North Korea’s only significant foreign financial centre.

‘They’ve got some tough decisions to make now,’ said one western diplomat. ‘Mr Kim seems to have been living quietly, but maybe it is not quietly enough ... with the focus that is now on North Korea, this is a potential hot potato for little Macau.’

However, his lifestyle raises other, longer-term questions. Given his jovial nature and late-night habits, there is nothing in his Macau existence that suggests any kind of political ambition. Mr Kim is a natural optimist, someone who likes to keep himself happy, according to sources quoted yesterday by one media outlet.

Those questions are bound to be raised over the next few weeks as Pyongyang celebrates the 65th birthday of ‘Dear Leader’ Kim Jong-il - one of the biggest events of the year on the North’s calendar of Stalinist pageantry.

North Korea has proved the only dynasty in the history of communism. Kim Jong-il was formally appointed by his father ‘Great Leader’ Kim Il-sung in 1974 - 20 years before he eventually took power on his father’s death in 1994.

Kim Jong-il has never made clear his own favoured successor, sparking widespread speculation that he felt humiliated by his son’s capture with a false passport at Tokyo’s Narita Airport in 2001. It was seen as the most serious in a string of errors in the eyes of his father.

Japanese and South Korean analysts have noted the lack of bodyguards when Kim Jong-nam travels as further evidence that he is no longer in serious contention for the leadership.

It is not known if Mr Kim saw his father during Kim Jong-il’s surprise visit to Guangzhou and Shenzhen in December 2005, an event seen as a mainland attempt to sell to its fraternal neighbour the benefits of economic reform.

A South Korean intelligence report presented to the South Korean parliament in December suggested the dynasty could end with Kim Jong-il. In the event of his sudden death, the report noted, it was most likely that top military officials would take over.

Yet Confucian ideals still weigh heavily across North Korea’s peculiar brand of Stalinism and few analysts have completely written off Mr Kim’s future potential as the eldest son. He has two half-brothers, Jong-chol, 23, and Jong-woon, 20, born to dancer Ko Yong-hui. Neither has emerged as a front-runner for succession.

Mr Kim was born to Kim Jong-il’s mistress, the well-known North Korean actress Sun Hae-rim.

Kim Jong-il’s relationship with Sun was secretive, meaning the young Jong-nam was isolated in his father’s most remote villas. Various accounts outline it as something of a gilded cage, with his father making up for his son’s isolation with lavish gifts and a vast playroom filled with the latest foreign toys.

By the time he was 10, he was packed off to study in Geneva and then Moscow, along with his mother and aunt. His mother eventually died in Moscow in 2002 after a long battle with depression. Her son spent a lot of time with her before she died.

Mr Kim is considered bright, mastering foreign languages as well as computer science. Returning to Pyongyang from his foreign studies, he held several senior positions in his father’s regime, including on a committee heading the feared domestic intelligence apparatus.

His highest profile posting came with his role as head of the Korea Computer Centre in the late 1990s. Mr Kim recognised the need to adapt and develop the latest information technology, such as voice-recognition software. The centre worked with South Korean firms yet was also linked to the development of a North Korean cyber warfare capability.

His interests in technology and computing have remained, yet Mr Kim appears to have no further direct links with the centre since his 2001 detention.

As he settles back down in Macau, diplomats believe Mr Kim is preparing to return to Pyongyang for his father’s birthday celebrations.

‘If he has any political future, the events of the next few weeks may provide some indication,’ said one foreign diplomat. ‘All eyes will be on Mr Kim and his brothers.’

The Stalinist pageantry now being prepared for the ceremonies could not be further removed from a late-night tot outside the Hang Van Loi Korean eatery in downtown Taipa.