I took this photo from inside the house.After mating for about 15 minutes, the male left (13:20). We could then had a closer look at the female. Eggs were visible through her thin abdominal skin. She looks velvety and heavy.
There are several British species of a few moth families showing this pattern of female flightlessness, amongst them the Winter Moth. The limited mobility of the females is compensated by the highly dispersive larvae, which might be able to balloon when little. In the UK adults are found from July to September.
On this photo you can see the vestigial wing: just a small hairy flap (the head is down and the abdominal tip up, egg laying).
At 16:41 she had pretty much finished laying.I searched around for more cocoons nearby and found one under a wooden shelf by a large cotoneaster, about 2 m away from the first one. It looked very fresh and translucent, and still contained a caterpillar.
The large oval cocoon and large caterpillar inside points to another female will emerge from this one too.