Anna and I both (separately) saw these very large moths flying around the garden late last night.
When I got up at 5am this morning, two had settled beneath a couple of our first floor window ledges.
A climb onto a stool to take the photo (not great I'm afraid) and a gentle poke with a bamboo pole, to show Anna these moths' incredible bright red underwings, and they were identified.
You'll not really mistake these though - there is no other moth in the UK with large grey wings this size - 4cm long at rest. You may see the brown caterpillars during the summer, but they only have one brood, and don't tend to fly like this until August.
When they feel threatened they will display that lovely bright red colouration on their underwings - ours obviously didn't feel that threatened!
Another nice moth to add to the Great Knollys Street list though!
The photo below is not mine, but does show the red-coloured underwings that I mentioned...