Urgent help required. Urgently.

Help! Unidentified 'pest' found under duvet!

Dear Blipfoto devotees,
I have today yet again discovered this animal in one of our beds. I've managed to get quite a good shot of it, please see picture, and I wonder if anyone has ever experienced the same or managed to successfully rid themselves of this problem?
Before you comment with the more obvious approaches, let me tell you I've tried everything. Boiling the bedsheets, biological washing powder, tumble drying, extensive hoovering, airing the room, that thing with an onion as suggested by my mother, pest sprays and I've even turned the mattress. I thought I was on top of the problem but here we are again today with one between the bedsheets.
I've contacted Rentokil but they don't want to know. 'Rats, or smaller' he said. It will answer to rat, I said, in fact to 'little rat', so that satisfies both of your criteria? He was not amused.
I'm not sure how much longer we can go on sharing our bed with this pest. Mr HH in desperation has taken to a sleeping bag on the floor, don't tell him but I've seen one in there too...
Yours, Mrs HH