As a political takeover it was one of the most soft-centred of military coups.

When General Prayuth Chan-ocha, head of Thailand's army and now acting prime minister, took control of the country last week he simply told the assembled politicians whom he had summoned to a central meeting point in Bangkok: "Everyone must sit still".

Later, when he addressed an astonished international community, Prayuth continued the soft-sell with further words of comfort. There was no mention of a "coup"; instead he declared that the military move was necessary "in order for the country to return to normality quickly, and for society to love and be at peace again … we ask the public not to panic and to carry on their lives normally."

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These were fine words spoken by a veteran soldier who is due to retire in September but, as the old saying goes, they butter no parsnips.

While the general was speaking to the outside world, the military crackdown was already in hand with the result that this weekend Thailand is firmly under the control of its army.

On Friday, using the pretext that he did not want Thailand to follow Ukraine's example, Prayuth imposed martial law, suspended the constitution and ordered 155 prominent intellectuals and political activists to surrender their passports.

In the same move he brought into custody former Prime Minister Yingluck Shinawatra who had already been ousted from her office by an earlier court ruling. Also taken into custody were several cabinet ministers as well as pro-government supporters and anti-government protest leaders in order to give them all "time to think".

This was the pivotal moment in what could still be a velvet revolution as many middle-class and urban Thais believe that Yingluck Shinawatra and her brother Thaksin are the sole authors of the current crisis and that nothing will be resolved until their grip on Thai politics has been broken once and for all.

By any standards theirs is an extraordinary story and one which demonstrates the truth of the adage that political power can often only be maintained by the use of corruption and the capacity to retain authority.

The Shinawatras have won every election in Thailand since 2001 and although Thaksin was forcibly removed from office five years later he still has a huge influence on the country's politics.

Indeed it has often been alleged that his sister Yingluck was little more than a proxy for him and his political interests, and that while she was in office he was still pulling the strings behind the scenes.

If that is the case it helps to explain the military's fear that the current crisis could very easily spill over into civil war between the old Thai establishment which remains loyal to the 86-year-old and ailing King Bhumibol Adulyadej and those favouring the upstart Shinawatra family which has made a fortune and gained huge political influence through Thaksin's activities in IT and global communications.

Tellingly, during his period as prime minister Thaksin attracted millions of supporters mainly from rural backgrounds and mostly from the poor and dispossessed who warmed to his populist policies and sensed an opportunity to assert their democratic rights in Thailand's caste-ridden society.

To them he is a hero not just because he seemed to be on their side but because he was a leader who appeared to be capable of reforming Thai society and freeing it from the centuries-old dependence on an aristocracy which in turn drew its authority from its relationship to the monarchy.

It mattered not that Thaksin had an indifferent record on human rights or that much of his wealth might have been gained through tax evasion and other financial scams. His supporters saw a leader who'd had to battle to stay in office and was finally ejected in 2006 by a court hearing involving questionable evidence.

Seen in that light, Thaksin was not regarded as a money launderer or a crook with dodgy associates but was hailed as a leader who understood the aspirations of Thailand's poorest and most vulnerable citizens. It also helps to explain the widespread dismay at the detention of his sister Yingluck who was elected prime minister in 2011 and who shares Thaksin's populist instincts.

Again, her indictment earlier this month on corruption charges involving rice subsidies was viewed by many as being politically motivated.

That understanding lies at the heart of the country's current problems. The Shinawatra family is divisive and has been involved in several high-profile scandals but many regard them as a force for the good and one that can end the cycle of corruption followed by military intervention that has blighted Thai politics in recent years.

It is a sorry fact that the country has now faced a total of 19 military coups, 12 successful, since it became a constitutional monarchy in 1932. The problem is made more pressing by the potential turmoil that exists over the Royal succession.

With King Bhumibol in a state of physical decline there are growing fears that the present difficulties could be exacerbated when he eventually dies.

The crown prince Maha Vajiralongkorn should be the favourite to succeed his father but under Thailand's constitution it is parliament's responsibility to proclaim the new monarch. When the time comes to choose, representatives could be swayed by the fact that not only does the 61-year-old crown prince have a playboy reputation but he is close to Thaksin and could form an alliance which would dominate Thai politics for many years to come.

For that reason there is a growing feeling within the royalist establishment that the crown prince has to be by-passed in the succession in favour of his more popular younger sister Sirindhorn. She would then rule as regent on behalf of the crown prince's young son Dipangkorn Rasmijoti, who would be named King Rama X.

At present these machinations are only conspiracy theories but given the army's repression of the media which makes public debate difficult they are real enough to the people of Thailand who are divided between the two rival factions - the anti-government yellow shirts and pro-government red shirts.

The only way out of the impasse is for the army to use this period of enforced "stillness" to broker an agreement which will lead to early elections - say within six months - but even that compromise could bring fresh problems. Due to the widespread popularity and economic muscle of the Shinawatra family, royalist supporters know that Thaksin or Yingluck would do very well at the ballot box. With both of them being inter-changeable in the minds of the many supporters the electoral outcome would be the same. That understanding also helps to explain the army's need to make a decisive intervention in the country's politics. It could be now or never.

"This is quite different from coups we've seen earlier. This is a one-in-a-hundred-years type of political crisis," says Ernest Bower, senior advisor at the Center for Strategic and International Studies, a Washington think-tank. "It's about who will be in power when the royal succession takes place."