I moved Colony 11 to another site in the hope that it would recover. I put honey in a feeder to bolster it. It didn't stop the robbing, although it did significantly reduce it.
Yesterday I plucked up courage and actually examined the comb in the brood area. There were no brood and I couldn't find a Queen. I decided that there was no point feeding wasps or other bees. It was time to combine Hive B (Colony 11) with Hive A (Colony 1).