Ever wondered why Port is traditionally 'Passed to the left' ?

One of those odd traditions we encounter from time to time. And given that may of us are about to enter the 'Christmas Do' period, i thought i'd try and find out just why we have this tradition.
Best i could come up with is this.
http://www.telegraph.co.uk/foodanddrink/foodanddrinknews/6231365/Pass-the-port-Why-do-you-pass-to-the-left.html