Londoners are the most likely to have a puff – almost one in 10. And if you're over 50, but under 65, the odds are even higher. Being a 55-year-old from Muswell Hill, north London, I am guilty on both charges. I started smoking weed at university, after going to see the Grateful Dead at the Rainbow Theatre in 1981, and have carried on almost ever since.

After uni I had to hide it from my parents. Then my wife and I had to hide it from the kids. Now the kids have flown the nest, and we don't have to hide it from anyone. We smoked more often back then; nowadays, it's no more than once or twice a week, maybe at the end of a dinner party, or to help us get to sleep.