Find out the facts before spouting garbage
Fermentation (conversion of carbohydrates to alcohol) is a process that can often occur naturally in the stomach. You simply need a starchy food (eg potatoes) and natural sugars in a slight acidic solution. This means that simply eating a potato with some fruit juice will start a fermentation process in your stomach and you will give trace values of alcohol in a blood sample. Zero alcohol limit means that EVERYBODY in this country would be banned from driving.
The police would not try to ascertain how many pints you have had to drink. They would just get the most accurate technology to register trace alcohol levels that naturally occur and claim they are doing their job. Zero alcohol levels are only going to EVER be bandied around by those who simply don't understand ANYTHING about biology.
If we use the analogy that somebody should not drive after having drank an alcoholic pint then what is the time frame you will put on this. Are you advocating that a person never be allowed to drive if they have ever had an alcoholic drink, ate a meal/desert that had alcohol in it? If you stipulate a time period that you could drive after having drank (4 hours, 4 days, 4 weeks and how would this vary for the amoutn drank or persons metabolism??), you have to accept that there would still be trace alcohol levels in some people and that would have nothing to do with wether they had inbibed an alcoholic beverage or not.