And, if you feel reasonably confident of passing a breath test, the answer tends to be “just the one”.
I recently concluded a poll asking the question “How many times have you been breath tested in your driving career?” There were 60 responses, and the results were:
Never: 23 (38%)
Once: 18 (30%)
Twice: 7 (12%)
3-5 times: 3 (5%)
6-10 times: 1 (2%)
More than 10 times: 1 (2%)
I have never held a driving licence: 7 (11%)
I was really asking this out of interest rather than trying to make any particular point. Obviously the likelihood of anyone being breath tested depends both on how long they have been driving and the pattern of journeys they make. I would imagine anyone routinely driving in suburban and urban fringe areas late on Friday and Saturday nights would have experienced more than one test.
While I am certainly not an advocate of large-scale random breath testing, there is no doubt that having been tested, or knowing a friend who has been, is an effective deterrent to drink-drive offending, and the widespread replacement of traffic police with speed cameras may in a sense have given a green light to offenders. But, given that most drivers rarely or never experience a test, it calls into question what safety benefit a lower limit would bring. If you just blend into the general flow of traffic, your chances of being pulled up are miniscule. Of course, though, the situation in which you are most likely to be tested is having just driven out of a pub car park.
For what it’s worth, I have held a driving licence since November 1976. Since then, I have driven more than 350,000 miles, and have been breath tested just once, almost exactly twenty years ago, in precisely the circumstances described above, having just pulled out of a pub car park in an urban fringe area at about 8.30 pm. I had had a drink, but an amount that I believed would leave me well below the legal limit, which the test confirmed.