Thai taboo: what happens when the king has gone?

He has led an extraordinary life. From his birth in Massachusetts, to the near-death moment at 21 when he crashed his Fiat Toppolino into the back of a braking truck on a road in Switzerland, to his mastering the jazz saxophone, he has the CV of an American or European prodigy. But all his achievements are overshadowed by the accident of his royal birth.

It is as King Bhumibol Adulyadej, avatar of the God Vishnu and much else besides, that he lies, aged 81, in Bangkok's Siriraj Hospital while his nation waits and prays. He has been under treatment for two weeks now. Thousands of visitors have stood in line to sign a book wishing him a speedy recovery. Across Thailand, events are being organised in his honour, with prayers read out.

The updates from the palace on the king's health strain to sound upbeat. The most recent said he was responding well to treatment for a slight fever and inflammation of the lungs. But as his hospitalisation draws out ever longer, there is growing anxiety not just for the well-being of the world's longest ruling head of state, but for the future of the country he has reigned over since 1946.

Many in Thailand revere the king, still considered by some to be semi-divine, and some commentators say he has acted as a unifying force in a country that is sometimes lacking social cohesion.

Only last month he voiced concern for the future of Thailand. "I am quite worried that our country is going to ruin because people have done things their own way," he said. "But if people are working together ... the country will prosper." As a constitutional monarch, he has done his best to use the charisma of his title to calm the country through its many crises.

However despite his position and enormous fortune, estimated at between $10bn and $20bn (£6.3bn-£13bn), his political role in Thailand has long been overshadowed by that of ambitious figures in the military.

There is the question of whether his anointed successor, the thrice-married Crown Prince Maha Vajiralongkorn, can live up to his ailing father's serene example. The monarch's long-drawn out hospital stay is breeding a growing sense of panic about the turmoil that could ensue should he die.

Harsh lèse majesté laws have been used so frequently to silence critics – sometimes with prison sentences of up to 15 years – that people are terrified of discussing this situation publicly. "The problems of succession cannot be discussed; they cannot be talked about in the Thai media," said a Bangkok-based analyst who declined to be named. "The issue of the royal succession has deepened the sense of crisis."

Thailand's political woes date from 2006 and most of them concentrate around the name of the man who was briefly owner of Manchester City football club, the telecommunications tycoon and former prime minister Thaksin Shinawatra.

Mr Thaksin became prime minister in 2001. Five years later, as fears grew that he was becoming too powerful and ambitious, widespread protests organised by a conservative coalition of army officers, royalists and business interests led to a military coup that resulted in his ouster and exile. When elections were held again in December 2007, an ally of Mr Thaksin was elected but both he, and a subsequent premier also allied to the tycoon, were also forced out – leading to clashes between the red-shirted supporters of Mr Thaksin and yellow-shirted conservatives – ardent monarchists who misleadingly called themselves the People's Alliance for Democracy.

The current prime minister, the Eton-educated Abhisit Vejjajiva, leader of the Democrat Party, was elected last December – Thailand's third premier in as many months. While Mr Abhisit is respected by many, his efforts to revive the economy have been hampered by violent protests and rifts within his six-party coalition. Experts say there appears no easy way out of the crisis that has polarised the country and dented the confidence of investors and tourists.

For although Mr Thaksin fled into exile to avoid a court conviction, neither he nor his red-shirted supporters have ever truly gone away.

Two weeks ago, as the King was taken ill, 20,000 red shirts gathered in the centre of Bangkok to protest on the third anniversary of the coup that forced from power the populist Mr Thaksin – who himself addressed the cheering crowds via a video-link.

This is not the first time that the king's poor health has thrown Thailand into turmoil.

In October 2007 he suffered the symptoms of a minor stroke, and last year was unable to make his traditional annual birthday speech. His daughter, Princess Sirindhorn, said he was weak and suffering from bronchitis and inflammation of the oesophagus. Then too, there were lines of well-wishers queuing at the hospital and commentators talking of the king's crucial position within Thai society.

Despite strenuous denials, not everyone believes the king has remained above politics. Many believe palace advisers were involved in the 2006 anti-Thaksin coup, and last year Queen Sirikit was criticised for attending the funeral of an anti-Thaksin campaigner killed during clashes with police. In the eyes of such critics, the king's death would remove the obstacle blocking Mr Thaksin's return to Thailand.

"Everyone is waiting for the king to die, because they think Thailand will enter a new stage," said Giles Ji Ungpakorn, an academic who fled to Britain after lèse majesté charges were brought against him. "Those red shirts think he is the most powerful man in Thailand and that when he dies there will be a power vacuum." But he added: "I actually think the king is weak politically."

Whether one believes that the king has acted as constitutional glue, or that he has blocked democratic change, many think his death, whenever it comes, will open the floodgates to change. Little wonder there is such anxiety in the kingdom.