From what has been said it seems the level being exceeded was half a pint of beer. I must I find that slightly difficult to believe but anyway, when I was being trained to fly, the received position was that half a pint is the lowest amount of alcohol that could - at that time - be detected. Nevertheless half a pint of beer produces quantifiable reduction in pilot performance under test.
Please, everyone, make sure you have a zero alcohol level when you fly.
I believe, by the way, that Tube drivers (and other Underground workers) are randomly breathylised and will fail if they have been drinking the night before - so no sympathy about intrusions on your lifestyle.