BIGGEST moth ever!!

Hey I'm just preparing tea and I spotted this mega huge moth (fortunately on the outside) on the kitchen window. I had to get a ruler to it as it seems to be about 4cm in body length. I like to look at it from here but I don't want to go outside and see it as I'm not keen on things that size and of the insect variety flapping round me!
Just look at the big fluffy body on it! Scary or what!


Wonder what sort it is.