DtG: never mind that, they give details for the average adult. The level below which you are considered 'safe to drive' (in the UK) is 80mg of alcohol per 100ml of blood.
Thus the standard idea of 4 'Units' = 2 pints of beer or 2 double scotches is based on the average person.
An average 'folkie' is probably noticeably heavier *BG* than the average 'normal person' and so will have a greater amount of blood in which to dilute the alcohol!
The use of the term 'lightweight' to describe a person incapable of holding their booze is probably surprisingly accurate.
Although most people have dificulty judging their own level of sobriety, an interesting experiment is to judge how you feel after a given number of your favourite tipple on succesive nights. Usually you will find that there is a point at which you can notice the effect on your speech or your actions. (If you can't see it, stop drinking now!!). Compare this standard (once noticed) with the level at which you get the same reaction after giving a blood donation. Your tolerance drops because there is more alcohol per unit of blood than would be usual at the same stage.

Nigel