As usual, I was out at dawn the other day and could see there was a dark shape in the pot of trailing pelargoniums by the front door. As it got lighter I found it was this butterfly which stayed there until the first rays of sunshine hit the pot then it left. I guess they have to spend the night somewhere - this just seemed rather exposed.
Probably not a typical roosting spot for the peacock, they usually conceal themselves in trees, shrubs, hedges etc where they will crawl under a leaf for the night. I have found them and red admiral in similar open areas to this before often in grassland habitats, presumably it got caught out by sudden cooling of the air.