It seems to me that, however careful you are, sometimes you bees are just going to swarm. In total we have 4 hives, three of them are just getting going and just beginning to lay down honey. We were aware that the other hive did seem stronger and has almost filled its first super but still had some space in the brood box for laying and, when last checked - 7 days ago- showed no signs of swarming. None at all. So imagine our surprise when, just as we were approaching the hives for this weeks inspection, we saw a great cloud of bees hanging in the air at head height. They soon settled on a fence post (see picture) and we quickly offered them the 'nuc' containing one of our newly acquired swarm wipes. Within 10 minutes they decided the nuc was a better option than the fence post and 'voila', box of bees.
We then turned our attention back to the hives to find out where the swarm had come from. (we were fairly sure it was one of ours as the only other local bees are still very weak from the bad winter). Sure enough, inside the strongest hive there are now queen cells, but still uncapped with big fat larvae inside. I would estimate the queen cells were about 5 days old which means that the queen swarmed well before the replacement queen cell was capped. So much for being ok with you check each week!
However, apart from the fact that we now have 2 hives in various stages of requeening, we are glad to have caught that swarm and it gives us an insurance policy in case any of the other hives do not requeen successfully.