Nor have the generals been shy about exercising their influence. There have been 18 coups in the 82 years since the end of absolute rule by the monarchy.

It was the army who terminated Thaksin's reign as prime minister in 2006. After being overthrown in a coup, Thaksin fled into exile to avoid corruption charges in 2008.

Two years later, protests against the unelected government that took power in Thaksin's place with the army's backing resulted in weeks of deadly riots convulsing the Thai capital. At least 90 people died and thousands were injured after soldiers opened fire on the protesters.

Now, it is Thaksin's sister and current prime minister, Yingluck Shinawatra, who faces being toppled by the military.

With central Bangkok blockaded by anti-government protesters trying to force Yingluck and Puea Thai to step down and the army leaving the capital's security to the police, whispers of a coup abound almost daily. Those rumours reached fever pitch last weekend, with reports that tanks and heavy artillery were being moved to Bangkok.

The protesters, a loose coalition of groups allied to the opposition Democrat Party and Thailand's traditional ruling elite, regard Yingluck as a mere proxy for Thaksin, who they despise for his alleged corruption and perceived disloyalty to the revered King Bhumibol Adulyadej.

Yingluck has called a snap general election for February 2 in a bid to end the demonstrations. But the protesters do not want a poll. Instead, they want the government replaced by an unelected "people's council".

With Thailand locked in a seemingly intractable political stalemate, many observers believe Yingluck's fate, and the future of Thailand's fragile democracy, now rests in the hands of the armed forces. And at first glance, the omens do not look promising for her.

Protest leader Suthep Thaugsuban, a rabble-rousing veteran politician, is believed to be backed by two retired army chiefs, General Prawit Wongsuwan and General Anupong Paochinda, who played a key role in the 2006 coup that ousted Thaksin.

The generals' support for the protesters has been prompted by the ongoing influence of Thaksin, and especially his reportedly close relationship with Crown Prince Maha Vajiralongkorn, the heir to the throne.

"This is all about the succession to the throne," said one source with close connections to the army high command who wished to remain anonymous. "Factions inside the palace, the army and the Democrat Party are concerned about what will happen after the succession. They think that Thaksin will be in control of all of Thailand because of his links to the crown prince. The generals are frightened by that. It would mean the end of the traditional elite."

Adding to Yingluck's apparent woes is the fact that the present army chief, General Prayuth Chan-ocha, is a protégé of Anupong.

Both men served in the Queen's Guard, an elite unit that owes its allegiance directly to the monarchy. The Queen's Guard is part of an army division known as the "Eastern Tigers", whose former officers now dominate the army's senior ranks and include Prawit.

Prayuth has issued a number of enigmatic statements about the military's possible role in resolving the political crisis. In December, he refused to rule out a coup, although last Saturday he backtracked from that statement.

"I think Prawit and Anupong are pressuring Prayuth to intervene because of the connections they have with him," said the source. "But Prayuth isn't bowing to the pressure. If he had, there would already have been a coup."

Prayuth's reluctance to mount a putsch stems in large part from the army's fear of a repeat of the violence of 2010, only on a far greater scale. Puea Thai commands huge support in the densely populated north and northeast of the country and the red shirts far outnumber the anti-government protesters.

"The army is still haunted by what happened in 2010," said Pitch Pongsawat, a professor of political science at Bangkok's Chulalongkorn University. "Staging a coup is the easy bit. The hard thing is the aftermath. The army knows the red shirts will come out and fight."

Some militant red shirts are reported to be stockpiling weapons and preparing to go underground if Yingluck is ousted. The army is already engaged in one guerrilla war against ethnic Malay Muslim separatists in the country's south. Having to fight the red shirts as well is an unattractive proposition.

"The army prides itself on its proximity to the people. They would find it mortifying to face even a symbolic backlash from large swathes of the Thai population," said Duncan McCargo, professor of Southeast Asian politics at Leeds University in the UK. "And most Thai soldiers are conscripts from the north and northeast, the heart of pro-Thaksin country."

Some of their commanders are Puea Thai supporters as well. They are known as "watermelon" officers, because they wear green combat uniforms on the outside but are red inside.

Yingluck has also been canny in her handling of the armed forces in an attempt to guarantee their support. Puea Thai has steadily increased the military's budget since taking power in 2011 - it rose by 5 per cent in 2013 alone - while no army personnel have been prosecuted for their roles in the suppression of the 2010 riots.

In a further effort to assert her control over the military, Yingluck appointed herself defence minister last July. "It allows her to have some say in meetings with the military and to be involved in some decision-making," said Pitch. "She does have some power over the military."

Perhaps the surest sign of Yingluck's confidence that there won't be a coup is the fact that she has been conducting government business at military bases since the protesters started laying siege to ministries.

On Wednesday, Yingluck met officials of the Election Commission at the Royal Thai Air Force headquarters. "She wouldn't do that if she was scared of the military," said Pitch. "I think a coup is unlikely now. I don't think the army wants to get involved."