There are some recent signs that expensive, synthetic cannabinoid-based drugs may get licensed here for an extremely limited set of medical circumstances, but I can't see British politicians going any further than that within my lifetime. The pace of change with regards to drug policy is maddeningly slow.
They're pro-legalisation, and if they still had 60+ seats in parliament they could be making real progress towards at least decriminalisation (probably under a labour coalition)
Every time people say "It doesn't" that sets back legalisation another 5 years.
It's very hard to prove causality, especially when marijuana's scheduling does not allow for proper scientific research.
Comparing anything to tobacco is weird because we spend considerable amounts of money trying to get people to stop smoking.
And we now have very good evidence that cannabis causes psychosis. That's pretty harmful.
From the NIH site on psychosis[0], about 3% of the US population in their lifetime[1]. About 100k adolescents annually have an episode.
For comparison, alcohol induced psychosis is common. Dependent alcoholics men face an 8x increase in risk; women see a 3x increase.[2]
[0] https://www.nimh.nih.gov/health/topics/schizophrenia/raise/r...
[1] worth noting that psychosis is not a "permanent" condition.
[2] https://en.wikipedia.org/wiki/Substance-induced_psychosis
The problem is that cannabis was never shown to be more harmful than tobacco scientifically in the first place, but the public and politicians were led to believe that it was. By the 1950s equivalents of "fake news".
You can see a similar "manufacture of risk" process going on with vaccines at the moment, which is very dangerous. It's also routine for the UK press to engage in ridiculously exaggerated anti-drugs campaigning, as it fits their sensational moralistic worldview.
Arguably more of a problem is the "we know this has risks but we can't feasibly ban it" category: alcohol.