They are, many believe, the statistics that say most about today's Scotland.

Fully 50,000 of this country's children are growing up in homes where there are drugs. Perhaps 100,000 more know an aunt, a brother or another close relative who is addicted.

These children are thought to be seven times more likely than the national average to develop a habit, a generational time bomb waiting to happen. Drugs are now so familiar it feels as if they have always been here. They haven't.

Less than 40 years ago, just as London and the South-east of England experienced the first wave of heroin, Scotland was effectively given the all-clear in a government report.

Professor Neil McKeganey of Glasgow University, Scotland's foremost authority on how narcotics are invading everyday life, said: "At the time that report was written the numbers of heroin addicts contacting drug treatment services in Scotland could be counted in double figures.

"Fast-forward 40 years and we find ourselves counting our drug users in the tens of thousands with around 12,000 starting drug abuse treatment every year.

"Scotland's heroin problem took off in the late eighties and in little more than 20 years has accelerated to twice the rate of the heroin problem in England. When you see something moving that fast you had better ask where it is heading. In the case of our drug problem the answer is pretty chilling."

The authorities believe they have started to keep the drugs industry under control. The overall number of known heroin users has been pegged back a few thousand in recent years and stands at 51,000.

Prof McKeganey, however, raises a more terrifying spectre: what happens if heroin use continues to rise at its historic trend of doubling every decade.

Heroin - and increasingly cocaine and new, stronger strains of cannabis - are already breaking out of the underworld. Many of the young men behind the bulk of violent crime are the children of the first great heroin epidemic in Scotland in the late 1980s.

In some parts of Scotland having a mother who is a addicted is no longer enough to warrant a child having his or her own social worker.

Prof McKeganey, however, warns it is not just children who are suffering. Any increase in the drugs industry will now start to eat into the very fabric of our society, our economy and politics, he believes.

He said: "There are millions of pounds being made each year from trade in illegal drugs in Scotland.

"The money from that trade often leaves Scotland to pass through numerous banking systems in other countries before returning as investments in legal enterprises.

"As this sequence unfolds we face the prospect at some point of being unable to distinguish between the legal and the illegal economy.

"At that point the drugs trade will have truly won respectability and permanence.

"What you might ask comes after the successful economics of the drugs trade? The answer is politics."

That, Prof McKeganey believes, makes drugs a bigger threat to Scotland than international terrorism.