It depends what spec they have as if they are more desirable you are going to get a lower discount.
Mine was listed at £34k 2 years old, pretty much fully loaded spec, and I paid cash. I got £3.5k off, so as good as 10%. Get the prices of every one for sale in a 100mile radius from the dealer and print it off, take it with you as a bargaining tool. Try to go mid week when they have lower foot fall and towards the end of the month as they are more likely to bend to get the deal closed.
Most importantly don't be afraid to walk away if the deal isn't right.