Thanks for the replies. Just to clarify, the small swarm I collected today I placed box and all in a medium super, toward the back of the super, with some sugar syrup, above an established colony, with the two separated by newspaper. Between opening the box with today's swarm in, and placing the lid on the lot, only a few of the swarm bees escaped. I am positive that the new swarm is in a bee proof super above the existing colony (the lid has screened vent holes, and sits proud of the super by 3mm(1/8th inch) all round).
The bees "clustering" are on the outside of the super, along one side and the back, concenrated around the vents and the gap. Either I left a bee size gap somewhere and today's swarm is out and sitting on the outside of another colony's house, or bees from the existing colony are taking a very keen interest in the intruders. By the way, I took my time closing up, and am sure that the super is bee proof, but it wouldn't be my first cockup. Is it common for the existing colony to show a large amount of interest in the new girls when combining, and is this likely to be what I am seeing?