The government's Chief Medical Officer, Sir Liam Donaldson, has urged ministers to cut the drink-drive limit to zero - but only for young drivers. For anyone older than 20, the current limit of 80mg per 100ml of blood will still apply.
At first glance, it seems like a good idea. Fewer young people will drink and drive, and we'll all be much safer.
But there's a very serious flaw in the plan. Even with the current 80mg limit, it's impossible to judge how much you can safely drink and still get behind the wheel. Every single piece of official advice says the same thing. I quote this from the Department for Transport's own website: "... the only safe option is not to drink alcohol if you plan to drive ... You can't calculate your alcohol limit, so don't try."
Unfortunately, if you have two separate limits in force, what you're doing is sending the message that it's somehow possible to tell between them. So whilst the under-21s might start to avoid alcohol completely when driving, older drivers will get the impression that it's alright for them to drink a little bit, so long as they stay within an 80mg limit which they can't possibly judge with any accuracy. Sir Liam may have his heart in the right place, but his comments seriously undermine the government's own campaign against drink-driving.
Just imagine the slogan - "Think! Don't drink more than a pint (give or take, depending on your height, weight, sex, ethnicity and personal alcohol tolerance) and drive."
Surely the right strategy would be to set a nominal but very low limit, perhaps half of the current one? It would be impossible to have an alcoholic drink worthy of the name and still be allowed to drive, but it would also protect people from getting arrested for having a trace level in their blood from a drink they'd had hours before. You could then send out a strong and consistent message to drivers of all ages: don't get behind the wheel unless you're completely sober.
This sort of thing happened during the debate on the smoking ban, and we're seeing it again. Government medical advisers may well be good at explaining the science to ministers, but they're extremely bad at coming up with actual policy!