Well, it worked! We went down to the hives earlier this week and had a quick look. Sure enough, there was a small patch of new brood in a very busy hive. We didn't look for the queen herself as it seemed pointless to upset the bees during the OSR season but we did take the opportunity to put on a super.
The original hive is obviously less busy - less bees - but there was fresh brood so the queen is still laying. We have decided not to unite these two hives. I have two queens arriving shortly and we will replace the original queen and then work on building up both colonies for the summer harvest.
We also did an artificial swarm with a second hive back at the house. It was packed with bees and brood but queen cells were there in force so we decided to deal with it in the same way.
In case you are wondering, the blue mark on the bottom of the hive means that we found and marked the queen. Blue was last year's colour - this year, 2011, is white.