The proceedings were kicked of by the Chairman of the Press Gallery, Brian Shallcross, and then the Speaker, Michael Martin, said a few words. Then it was Dad's turn, who began by remarking: 'This bar must be unique in history in that is has been formally opened by a teetotaller, and named after a man who hasn't had strong drink for a quarter of a century. Despite that I have every confidence that this bar will live up to the disreputable reputation of its predecessors.'
He went on to recount some of the most famous feats of drinking and debauchery to have occurred in the previous incarnations of the Press Gallery bar. You can hear his full speech here.

There was an article about all this in the Independent a couple of weeks ago - here.
My other photos of this event are here. Sorry, they're pretty terrible.
18/12/2007 Edit: another article and better photo here.