Why is the UK government still so anti pot? Is it because of anti drug propaganda? ?

I noticed there's a lot of plain incorrect things said about legalized marijuana in the UK papers, especially that it contributes to car accidents. We Californians haven't had an increase in drivers being under the influence, just drivers testing positive which you can for up to 30 days after smoking. But in the UK that's all it takes to lose your drivers license, job, income, and maybe even house. From our perspective seems really cruel when your police and newspapers brag about how many drivers they've banned or people they've locked up over positive drug tests.