I doubt that it is beyond science Andy. But every man and his wife will run that defence which will cost thousands on legal aid (for those that qualify). At the very least it will result in blood tests being required rather than standard breath tests - again a huge cost. And for what benefit? I would be interested in any statistics where drivers under the limit were involved in accidents where drink was a significant factor (apart from the one cited in the article).
Whilst I agree that it should be zero, I think on a purely practical level setting the level significantly lower, but more than 0 should knock out the "mouth freshener, sherry trifle, cough medicine, occurring naturally etc" defences. I would have thought it is possible to set a level of (say) 5mg - as opposed to the current level of 35mg.
The article proposes 20mg in blood (currently it's 80) and I'd say that that was entirely reasonable. In my view (and it is only a guess, I have no empirical data) that would probably avoid prosecution of those where it does occur naturally, mouth wash etc but would automatically catch anyone who has actually consumed alcohol - however long before it was. The boffins would need to look carefully at the levels first.
We have to look at the mischief the law is there for - it is there to make the roads safer. If someone can lose their licence, home and career for having over indulged on the Listerine that is wrong. However, if they go out and drink and CHOOSE to drive, that is entirely proper.