Think you'll find 2.5 times the limit isn't the amount you have drunk over an evening its the amount present in your blood at that moment in time so in your example it would be the same as you having 4.5 pints in one go directly into your blood without any metabolism of the alcohol. When you drink 4.5 pints you would do so over 3-4 hours i'd guess and your body would be processing and removing that all the time
Someone talking some sense at last.