I'm very surprised that a used Nissan bought from a main dealer doesn't come with at least 1 year's warranty, and I've never heard of any main dealer for any brand offering a car for sale with less. That said, it's all down to what it says on the paperwork you signed I guess.
£1100 is a rip-off though, even if they're doing both slave and master (while you're there, I certainly would) I would expect a bill of around £800 at the most. Go and speak with the guys in Chester, they seem far more clued up and willing to help.