When I was at school we had one period a week dedicated to a talk on something non-academic.

It could be about choosing careers, drawing up a CV, the evils of bullying or glue-sniffing, the importance of condoms and the like.

Drug abuse came up more than once. And cannabis was always firmly condemned.

It might not be very harmful in itself, it was conceded - and no more addictive than caffeine. But it could lead to the abuse of harder, more dangerous drugs.

I never really bought this. By the same argument, we would ban half-pints of cider on the grounds that they could lead on to drinking methylated spirits. They may do for some people, but not for most.

Later I met people who had smoked cannabis but would never dream of touching heroin, crack cocaine or anything more harmful.

I've never smoked it myself for the same reason I don't smoke cigarettes. Cancer frightens me too much.

And I'm all for public health warnings against smoking, heavy drinking, over-eating and other risky behaviour. But if people refuse to heed them, then we have to leave them to it, as long as they aren't harming others. It's their funeral.

What seems clear, however, is that for some people cannabis does more good than harm.

And 12-year-old Billy Caldwell is one beneficiary. Billy's severe epilepsy can be treated with cannabis oil, but when his mother tried to bring it into the country it was confiscated at the airport. His seizures intensified and Billy ended up in hospital.

Doctors protested, and so Home Secretary Sajid Javid allowed the return of the substance to deal with what was a medical emergency. And he's promised a review into the use of cannabis as medicine.

So the pros and cons of legalising cannabis are being revisited. I reckon the pros easily outweigh the cons.

So does William Hague. When he was Tory leader he advocated a zero-tolerance approach to cannabis, but now he admits he's changed his mind.

The evidence seems pretty clear. A report by development organisation Health Poverty Action says that if cannabis were legalised and regulated in Britain it could bring in up to £3.5 billion a year in tax revenues.

Maybe that money could plug the gap in the NHS budget without some of those tax rises Theresa May has warned us about this week.

Relaxing the ban in some of the US states that border Mexico has led to a sharp reduction in violent crime. Farmers are allowed to grow it - taking it out of the hands of the drug cartels that controlled it.

A policy that brings in billions in tax revenue and cuts violent crime - and might free up the police and courts to deal with more serious offences - seems like a no-brainer.

In fact an argument could be made for decriminalising all drugs. It has worked very well in Portugal.

Drugs are now treated there as a public health issue rather than a criminal one. Money that used to be spent on prosecutions now goes towards treating addicts.

A dramatic rise in drug use, which some predicted, failed to materialise.

And now drugs there hardly kill anyone. In 2015 there were three deaths caused by overdoses for every one million people in Portugal.

The average in other EU countries is 17.3 deaths per million. In Britain it is 44.6 per million.

Last year Norway decided to follow Portugal's lead.

But ideas that make perfect sense always meet with irrational resistance - whether it's the plastic bag charge, the indoor smoking ban or even many years ago the breathalyser.

And politicians are too terrified of doing anything that might allow the Daily Mail to accuse them of being soft on drugs. The Lib Dems and the Greens back a change but Labour and the Conservatives don't.

In 2002 the then Home Secretary David Blunkett downgraded cannabis to Class C, but five years later it was upped to Class B again.

When first elected to parliament David Cameron backed more lenient penalties for possession of cannabis and ecstasy, and suggested heroin should be prescribed to addicts. But when he became prime minister he dropped those views.

This year we celebrate 100 years since the end of World War One. That war began in 1914 - and another war was declared that same year, the war on drugs.

The world war was concluded within four years but the war on drugs is still being waged and there's no end in sight.

Maybe it's time to call a ceasefire. Dropping the unenforceable cannabis ban would be one way to reduce hostilities.

But will any of our politicians have the nerve to do so?