What could be Britain’s highest growth industry of the next decade? There is no shortage of plausible candidates. Driver-less cars could turn into a vast new industry for the first country to get its roads and legal system ready for them.

Robotics has the potential to be far bigger than computing, given the range of tasks that machines driven by artificial intelligence could perform. Biotechnology has been around for a couple of decades, without quite living up to its hype, but no country has a stronger tradition in medical technology than the UK, and could yet make some stunning breakthroughs.

But if we decided we wanted it, it could be something that no one is thinking of right now. Legalised marijuana. In the United States, the drug is being gradually legalised state by state. Slowly, some figures are starting to emerge on the economic impact of that – and it is huge.

In fact, legalised marijuana has the potential to be a massive industry, creating tens of thousands of jobs, and billions in tax revenues. Of course, it is perfectly reasonable to argue that we should maintain the blanket ban on the drug on ethical and moral grounds. But at the very least we should be aware that we are ignoring some large potential economic gains from legalisation – and take that into account in making that decision.