He Lives!

 I'm going to call him Lazarus. I spoke too soon when I said the caterpillar-not-a-pear-stalk was dead.
Last night, when I went into the kitchen to make my bedtime drink I noticed it had moved position - and was still moving.  I bunged a veritable salad from the frig into the box, hoping that there would be something to keep it happy for the next few hours.
But I still don't know what it is, despite Pleach's suggestion, the latest thought is that it might be a Peppered Moth (Biston betularia), which feeds on Birch, Oak, Rose, Bramble, Willow, Elm and Hawthorn, none of which have I yet provided; in the photo it seems to eating cauliflower leaves. 
So, excuse me, I'm just off with a torch and umbrella to raid the garden...