Our back door has stopped opening. We think the cylindrical spinning thing in the middle of the bit that goes in the hole on the door frame when you lock it has slipped down and stuck the door locked (as this happened once before when the door was open). Any ideas what we can do, or is it a locksmith job? If it is a locksmith job, advice on better terminology so I sound like less of a tit would be appreciated. There's only a hole for a key on one side of the door. It happened when Mr Oula was smoking in the garden. Luckily I was still awake to let him in the front door as he was in his pajamas with no keys.