I have read the above posts with interest. Searching Google - I found the following :-
http://www.80mg.org.uk/guide.html
As TC says, determining how alcohol will effect you will differ from person to person - though, the above site recommends that men should not consume more that 4 units immediately before driving. Excess of this runs the risk of being over the legal limit.
The following .gov link states that a small double measure of Spirits = 2 units
http://www.knowyourlimits.gov.uk/units.html
Considering this, I would think that Scott was a lot closer to the legal limit than he thinks he was. I agree with the consensus, you appear to have been very lucky, Scott.