"We are marching to Government House," a speaker declared, revving up the members of the United Front for Democracy Against Dictatorship, a group loyal to the ousted former prime minister Thaksin Shinawatra. "The military has already seized it."

Inside the Government House compound, 18 military units were in place, waiting with understated menace behind police lines.

No one would argue with the army's right to defend the seat of Thai democratic power from a mob. But late last year when the pro-monarchy People's Alliance for Democracy, dressed in the King's yellow colour, stormed and occupied the same compound, and shut the country's two busiest airports, the army made no move to defend government interests.

General Anupong Paochinda, the head of the army, went so far as to say: "I am not a soldier of the Government. The army belongs to the Thai public. I can't channel it to serve as anybody's private army."

The democratically elected government, without the support of the security forces, collapsed within months.

"The military many times make coups," one Red Shirt protester, Malesh, said. "They are still behind all the governments except the government of Thaksin."

Eighteen times since 1932, the end of absolute monarchy, the army has intervened - most recently in 2006, when the generals ousted Thaksin.

However, coups are not what they used to be. The military has learnt more can be achieved one step back from the levers of power: it wants the world to believe it has retired to barracks and left Thailand to the mercy of politicians.

The new Prime Minister, Abhisit Vejjajiva, has made no public appearances with General Anupong since taking power. He is a reassuring figure for the West, speaking of change and the importance of democratic rule. There is only one problem: he resoundingly lost the 2007 election and gained power only with the assistance of the military.

Mr Abhisit's fragile coalition government was cobbled together only after General Anupong did some serious arm-twisting of pro-Thaksin MPs.

In an interview with the Herald, Colonel Sansern Kaewkamnerd, the army spokesman, sought to downplay this influence. "With forming the government coalition, many political parties came to us and asked for our opinion, creating the impression the army was the institution behind the forming of the government. This was not the case."

A Western diplomat based in Bangkok was more blunt. "The military is on the front line of politics here; no government in the forseeable future of either side will be free of their influence," he said. "They have a significant role in security, politics and economy - and that is no different under Abhisit."

Behind the scenes, General Prem Tinsulanonda, the head of the King's advisory Privy Council, a former army chief and long-time prime minister, is widely regarded as Thailand's second most influential man, behind the monarch. General Anupong, the current Thai Army chief, is arguably No. 3. Only then comes Mr Abhisit.

Before 2006, the army had been steadily losing influence, damaged by a coup in 1991 that ended in ignominy after bloody clashes left hundreds dead. Its funding under democratically elected governments plummeted.

But the national budget tells the story of its resurgence. Since the 2006 coup, and with Thaksin gone, its allocation has almost doubled from 88 billion baht ($3.8 billion) in 2006 to 167 billion baht in 2009.

Colonel Sansern said everyone learnt a lesson from last year's airport disruptions. "The army made an experiment, to test the system, to see if the government mechanism could solve the problem." Asked whether it had worked, he nodded towards a closed-circuit TV feed of the Red Shirts surrounding Government House. "What do you think?"

In this climate, the space for dissent is becoming increasingly constrained. The lese majeste law, which forbids insulting the royal family, has become a key instrument for control.

There are 117 Thais facing lese majeste charges.

"This is going to last a long time," Thitinan Pongsudhirak, director of Chulalongkorn University's Institute of Security and International Studies, said. "There is a climate of fear and paranoia which will last for years, not weeks or months.

"The middle ground has vanished in Thai society. There is polarisation and confrontation, there is a greater likelihood of clashes. The two sides are entrenched. The question for Abhisit is, can he hold it together?"

Connie Levett flew to Thailand courtesy of the Royal Thai Consulate in Sydney.