Hang in there Leigh. It is frustrating that our weight fluctuates so much when we are all trying to lose, but I think both the fact that you indulged a little more and that next week is TOM will explain the gain and it will disappear after next week if you stick to the plan. This happens to me too, even when I have been really good, the week before my period I always gain or maintain but have a massive loss (3 to 4 lb) the following week. Congrats on the magic milestone of the next stone bracket - it will reappear I assure you.
It is always harder when that little gain puts us over a major milestone we have been so proud to achieve, but don't give up. Soon you will be under 11 st again, so take a good look at the horrible 11 and perhaps this is the last time you will ever see that number on the scale!