Hi again Ism:
Okay, doesn't sound too promising. However, have you either spoken to the salesman again or his boss? If not, it may well be that it slipped his mind, far fetched though that may seem.
I mean, if you've just bought a brand new car and have obviously spent thousands of pounds on it, it sounds reasonable to assume that you wouldn't be "nit picking" just to get �400 knocked off? Therefore, if the salesman won't play ball, demand a face to face meeting with his boss to try to get some kind of resolution.
If you don't ask, you won't get?