There was still honey stores, so food hadn't been the problem - but it looked like there had been recent Queen cells, so maybe they had created a new Queen and she hadn't survived her maiden flight due the the number of Asian Hornets about ? If she didn't make it back, the rest of the bees wouldn' survive. All a bit of a mystery...
Will have to try and repopulate it come spring.
The other two hives were fine - The bees there have survived the recent cold weather - they are out and about as soon as the sun comes out.
I've just put some "Candy", special lump sugar based fondant enriched with vitamins, inside the two healthy hives. It's in a plastic wallet, that you have to cut into so the bees can access the food. Hopefully that will see them through to the spring.
Also made an exciting purchase - 84 glass jars with new lids, featuring bees on a honeycomb pattern. I try and recycle jam jars for most of my honey, but last year it got really hard to keep up with the quantity required, hence decision to bulk buy a load : this is what my honey will be in next year :
Fingers crossed the candy does the trick, and I have at least two healthy hives come springtime!