Would armed troops from the People's Liberation Army garrison have headed for Chek Lap Kok and demanded the right to hold the US spy plane and its crew, citing Article 5(4) of the Garrison Law, which gives them jurisdiction over all 'foreign-related military affairs'? After all, there is no doubt this is a matter which falls within China's remit under the Basic Law, not least because every arrival of a US military aircraft requires prior approval from Beijing.

Or would Hong Kong's Secretary for Security Regina Ip Lau Suk-yee - who never seems to miss any chance to burnish her credentials with Beijing - have found some other obscure legal provision to justify holding the aircraft and crew?

Most likely, neither of these extreme scenarios would arise. Holding hostage those involved in an accident is hardly acceptable behaviour in Hong Kong, and the crew, at least, would almost certainly have been quickly allowed to return home to the US. After all, there are limits beyond which even Ms Ip will not go - as shown by the fact that, despite all her ridiculous rhetoric on the issue, she has made no move to ban Falun Gong.

And the PLA, having gone to such lengths to ease fears about its presence by keeping a low profile since the handover, would be unlikely to take a step which would have such a devastating effect on Hong Kong's international image.

But the alternative would have been just as damaging to Hong Kong's domestic image. After all the outrage that has erupted on the mainland over the fate of pilot Wang Wei, imagine the anger there would have been if the spy plane with which he collided had been allowed to land in a city that is part of China - albeit operating under a different system - and then freely continue back to the US. No doubt, some in Beijing would have begun to wonder if the SAR needs to be put on a tighter leash.

Either way, Hong Kong's autonomy would have been put to the test by the arrival of the spy plane.

This time, an accident of geography meant the SAR was not involved. But it cannot rely on always being so fortunate in future. Sooner or later, some other issue is bound to arise where Hong Kong faces a straight choice between its autonomy and an issue so vital to Beijing that it will make the recent row over Falun Gong's local activities seem like a storm in a tea cup.

Arguably, one is already looming, since many expect Canada to deport China's most-wanted fugitive to Hong Kong, placing the SAR in the difficult position of choosing between sending Lai Changxing on to face certain execution on the mainland or incurring Beijing's wrath by refusing to do so.

But whatever the issue and whenever it arises, the repeated incompetence of Tung Chee-hwa and his administration since the handover leaves little room for optimism that they will handle it in a wise manner.

Danny Gittings is the Post's Editorial Pages Editor