At last I will explain what happened to 2 of our beloved chickens. In short, a fox got them.
We'd been allowing them out of their run as they really liked being outside. At the end of November we let them out one morning and within 10 minutes 2 of them had been killed. I only managed to rescue 2 of them by getting them into the kitchen away from the evil fox that was scampering around our garden, feasting on our darlings.
A lesson has been learnt.
So with FrouFrou and Henrietta dead, Trixie and Antoinette are cold and lonely. Thank goodness they have each other. We've applied to get a couple more chickens as it's only fair on them to be in a small flock. Hopefully we can extend their run too so that they have more freedom.