Like the other foreign correspondents living in Bangkok I would face years in jail if I wrote or said anything deemed to insult, defame or threaten the king, queen or heir apparent.

King Bhumibol Adulyadej is not himself a great fan of the laws. On the occasion of his birthday in 2005, he cited the historical British phrase that "the king can do no wrong".

"But the king can do wrong," he said, arguing that when the monarch is not subject to criticism he is "in trouble".

Successive Thai governments – the king's extraordinary reign, stretching back to June 1946, has spanned 29 prime ministers -  have however maintained the laws that provide for 15 years' jail for each lèse-majesté offence.

The laws are interpreted broadly and scores of Thais have been convicted and jailed in recent years.

What I can say is that a pall of anxiety is now cast across the country of 64 million people over the declining health of the king, the world's longest-ruling monarch, who is 88.

He was last seen in public in January.

Medical bulletins detailing his ailments are read with concern.  The Royal Palace announced on Wednesday that the king's kidneys are still not functioning properly but that infections he had been suffering have eased.

Worrying news from the palace often sees a drop in the Thai stock market, reflecting the concern people feel for their monarch.

Some Thais are praying for the king using a Buddhist rite normally used for terminally ill patients.

Anxieties over the king's health and the succession have formed the backdrop to more than a decade of bitter political division in Thailand that has included military takeovers and sometimes violent street demonstrations.

In his 70 years on the throne the king has presided over the revival of a faltering centuries-old royal institution, growing in power and influence as he helped direct Thailand's social and economic development.

His picture hangs in many Thai homes and offices, and Thais stand in respect when a video of him is shown in movie theatres. They prostrate themselves before members of the royal family.

Some Thais see the king as semi-divine. Schools teach respect for the king and the notion of his near-infallibility and beneficence.

The heir apparent is King Bhumibol's only son, 63-year-old Crown Prince Maha Vajiralongkorn, a military officer who trained in Australia. The king designated him crown prince in 1972.

Under the Thai constitution, a princess could accede to the throne in some circumstances, including the king's second-born daughter Princess Maha Chakri Sirindhorn, who is linked to royal charities, arts, education and religion.

Thailand's Privy Council, a body comprising elderly counsellors appointed by the king, will nominate the successor to cabinet and parliament. It is a choice that will shape the future of Thailand's constitutional monarchy and the nation itself.