It wasn't as strong as the other to start with and was I think in need of some help. So I decided to take the pressure off the larger one and help the other.
The small hive was occupying maybe two frames whereas the bigger one was on almost all the frames in the brood box. I took a full frame of stores and a frame of brood across to the small hive.
I think this will boost bee numbers and also allow the new bees to grow in a period where forage may be hard to come by. Today it has been raining constantly so I think my decision was vindicated!
We shall see! I'll check in a week or so.