So, this is what a Red Admiral looks like in repose. I thought it was in a sorry state, but then I researched online and saw other photos of Red Admirals resting and their wings really do look this tatty when they are closed. I suspected it was a Red Admiral because of the flashes of red and white, which correspond with the white stripe and dot, and a glimpse of part of the bright red stripe, though not the red edge, on the other side. Red Admirals are quite common and like a variety of habitats. The caterpillars particularly enjoy eating nettles and we do have a nettlebed and a good scattering of nettles in the watermeadow.
Update – I was able to photograph a Red Admiral with its wings outstretched. I just had to wait patiently for a while. It turned upside-down before it flew off!