Zero would not work and be too draconian. As much as it takes your body one hour to process one unit of alcohol, it will still take 24 hours for your body to be totally clear and pass a drink driving limit of zero.
So imagine what that would do to the lifesytle in this country? Everybody who drives to work would not be able to drink from Sunday right through to Friday night (or Saturday if you work on Saturday or are going shopping/visiting). Perhaps you plan to drive somewhere on Sunday as well? In that case, you will have to become a teetotal except when on holidays.
Apart from the fact that I could see that most people would then break the law and have a glass of wine or other drink with their meal, the pub and drink industry in this country would be decimated.
Also because most people would break the law and still have a drink the night before, the police would be almost guranteed a result for everybody they stopped so expect millions of people losing their licence for a year (or until people realise and become teetotal or there is such a backlash, the law gets changed). So you may as well ban drivers from being allowed to buy alcohol.
Throw in that some medicine contains very small amounts of alcohol, shandy (the tinned drinks) and you have major problems.
The country would become a disaster. As much as I don't condone drink driving and anybody caught deserves what they get, remember more people are killed in road accidents due to tiredness than drink driving nowadays.
Having systems which limited how many hours you can drive a car or how long since you drove it (to allow for a sufficient rest period) and forcing you to stop every two hours would do far more good than a zero drink driving policy.