The Assad regime is now clearly beginning to crumble. The defection this week of the Syrian ambassador to Iraq, coming only days after the flight of a top general who was once an Assad confidante, both signal the advancing disintegration of the dictatorship.

Nawaf Fares was not simply his country’s top diplomat in Baghdad but he is also the head of the Uqaydat tribe,whose homeland is in eastern Syria and across the border in Iraq. His defection to the rebels will almost certainly boost the existing insurrection in this tribal area.

In his statement announcing that he had quit, Fares said that he could not carry on supporting a regime that was oppressing its people. The opposition will be hoping that the ambassador’s abandonment of the regime will now be duplicated at other Syrian missions around the world.

It is important to try and work out why major figures like Fares choose any particular moment to quit. Fares may have been under pressure from his tribe. Alternatively, he may have concluded that because of the rebellion around the regional city of Deir Al-Zour, his own standing with the regime was compromised and he was himself in danger.

What is harder to believe is that after 16 months of steadily rising violence, Fares suddenly found he could no longer support his president. As a top diplomat, he and his family would have enjoyed the privileges and wealth reserved for the regime’s elite. Maybe he had to ensure that relatives were safe from retribution before he made his move and also had to move money out of formal bank accounts. All that can take time, if it is to be done without attracting the attention of the secret police and the authorities.

Then of course there is the more fundamental reason for any official to defect - a reason that will certainly be prompting future defections - and that is the fear of being caught on the losing side. Those who stay loyal to Assad to the end can expect some sort of retribution. Those who quit the regime in its final hours will perhaps be treated with even greater contempt, because they were happy to stay until the last minute and then quit to save their own skins.

There is thus a tipping point for would-be defectors, beyond which their reasons for quitting will be less than convincing and that point may well be approaching.

Apart from those who joined the insurrection early, there are few obvious heroes among the defectors. An exception may be the commander of an elite Republican Guard formation, Brigadier General Manaf Tlass, who reportedly protested to Assad himself at the violent suppression of protestors. As a result he was effectively placed under house arrest, though nominally continued to hold his command. Assad may have acted out of friendship or fear of revealing such a high level protest. Either way, it was a bad mistake. Tlass and some of his officers and men fled to Turkey.