When bad things happen in China, and people say bad things about it, somehow it makes me want to look on the good side of the place. I got into a row with Damian Thompson, another Telegraph blogger, on the subject the other day, and found myself defending the place, or at least sort of.

Then something undoubtedly good happens, and it just alerts me to the seedy and creepy undercarriage. I'm sorry, but that's just how it is.

The good thing is this: Chinese doctors have just promised to end the practice of using the organs of executed prisoners for transplant operations.

That's been the subject of a long campaign, and I've written extensively on it here on the blog and in the newspaper, on one occasion finding myself agreeing to be a middle man selling prisoners' kidneys and livers to British patients for tens of thousands of pounds.

That this is a step forward is clear: the news comes from the Chinese Medical Association, a government-backed body, and the decision was made, we are told, with the backing of the ministry of health. And so that's it: an end to all those stories about foreigners, Hong Kongers and Taiwanese, and mainlanders too, spending vast sums of money without thinking too hard about how their new organs got from donor to the recipient via the execution ground.

The trouble is, we don't really know for sure that this is what is going to happen. No dates have been given for this to come into force, and, as I've explained before, it's never quite clear whether ministry of health edicts cover the military hospitals, where a lot of these operations take place (though I'm assured that on this occasion it does).

Doctors say that the number of such operations is already in rapid decline, partly due to a ban already announced on the sale of organs to foreigners.

The number of executions is also well down - from three or four thousand cases registered by Amnesty International until a couple of years ago to 1,600-1,800 for the last couple of years. We know the real number is probably a lot more than that - but even that total figure is supposed to be declining as well.

But that just serves to make me suspicious. What if the reason that the number of executions going down is because, well, hospitals can no longer use their victims' organs so readily to make money? Rather proves the point that these people were being executed to order, doesn't it?

Well, that's a bit of a logical leap, I'll agree: it's entirely possible that humanitarians in the Party apparatus - including, perhaps, the non-Communist Party member and foreign-trained new health minister - have decided out of basic human values both to restrict the execution rate and to stop the sale of prisoners' organs.

Nevertheless, the changes make me realise how little we truly know about this practice, which has gone on for two decades and has provided organs for tens, possibly hundreds of thousands of people. Hidden behind the veil of relatives' anonymity, and police and army practices (corpses were often cremated before being returned to the families); and hidden of course behind the whole secretive apparatus of the state, the police, and the PLA (and their hospitals), we still do not know who these prisoners were, how many of them there were, what they were convicted of.

A couple of exiles have given graphic personal testimony, but that's old now, and doesn't go to the wider picture.
I have criticised before the wild claims from a year and a half ago by Falun Gong, the religious cult, that 6,000 adherents were culled in a single death camp in Shenyang to feed the trade: few took the claims seriously, except a couple of human rights activists in Canada (albeit ones with a bit of standing).

But those activists raised enough questions to want answers, that we are unlikely ever to get: was there really a surge in transplants, as was claimed, in early 2006, and if so, why? Why do figures for the number of annual transplants so far exceed the number of known prisoners executed, if nearly all organs come from prisoners, as everyone agrees? Why were the activists, on taped phone calls, told so readily that the organs would come from falun gong followers?

There are good people in government in China, and at every level of society. But there is a very black underside, which is only ever partially glimpsed.

This is one of them. One can but hope that the "is" is now a "was".