I am absolutely livid with myself. Obviously too distracted at the time and had somehow bundled it up with similar coloured towels, so it was washed on a 60c wash 
It was brand new, a lovely green wool jumper, and a Christmas present from DH. It's now very small and has felted.
I've actually had a little cry at my stupidity and bloody awful waste of money.
Do I own up or just quietly shove it in the back of the wardrobe? He'd honestly never notice... Oh god, now I'm deceitful as well as inept!