andrea81 ... I agree.
You don't need to change the law. You need to make jolly sure that people start obeying the law as it is. How? Greater penalites for drivers who don't.
The limit is there. It is low. Stick to it. If you don't stick to it, then you will be punished.
But don't punish those of us who do stick to it. Lots of us, if we are driving, I will have a drink. But we won't have two or three because (1) we might go over the limit, and (2) we are responsible drivers. Leave us alone. Do not turn us into criminals. Concentrate on the bloke in the other car who has had five or six, and who is heading off to smash some kids legs. He won't give a stuff if you reduce the limit. He's too p**sed to worry.
The question is not how to turn the "one pint" people into criminals, but how to catch the "five pint" people.