I've been floating between 14 stone 13lbs and 15 stone 6lbs for about the last month Harry so I know exactly how you feel. I wish I could be as determined as you and be sure that there will be no more alcohol, and no more breaks etc, until Christmas. But I know that it simply won't happen - a horrible time of the year for dieting!
Enjoy your dinner and celebrations tonight, make wise choices, and get straight back on it tomorrow morning!