Thanks for your suggestions, and my sympathy to fellow sufferers. These are Warre hives with solid floors, well propolised and pretty airtight. The entrances are closed down to a bee space or two, and there is a stream of moisture on the landing board each morning -a mini ice rink today. I have put mesh over the entrances for the night.
Today I deployed bottle traps, and my fingers and thumbs were busy too and so there will be a hundred or so less of the buggers tomorrow. I have again searched in vain for nests, but there are walled and fenced gardens nearby.
I have to admire jasper anatomy. Flying from dawn to dusk at temperatures near to freezing. Fast and crafty dodging when sneaking in to hives, wrestling with several bees and flying off when ejected, and needing considerable force to squash, making off after a near-miss prod that would flatten a bee.