I've been visiting the hives in central Oxford every couple of weeks. There is still evidence of activity on the base board in all 6 hives (chewed cappings; dead Varroa; etc). I believe that they're all still alive and ok.
There are causes for concern though. All the hives have visible numbers of dead bees at their entrances. I don't know whether these were healthy bees which were stranded during cold weather or whether they were virus infected bees which crawled out of the hive. I presume the latter.