We have already had to split our hive to try to stop them swarming - I went out yesterday to get some photos and found that they had swarmed anyway. Needless to say that the camera got forgotten about in the panic that followed!
Luckily the bees hadn't swarmed far and were still in our yard on several plant pots and the table. After coaxing them into a cardboard box with a helping brush from the feather duster, the bees were successfully restored to their hive and so far, they have not swarmed again.
So we now have two hives of bees to look after, assuming the don't swarm again!