Okay I got one of these mousetraps and so the battle of wits between human and rodent begins. At the moment it's 1-0 to the mouse.
I added the bait (some Chocolate Buttons) and placed the trap behind the settee that I'd seen the mouse emerge from before. Unfortunately my dog likes choclate too and rather impressively he managed to squeeze in behind the settee pull out the trap and open it.
So I am now out of bait and in need of a dog free place to set the trap.