As far as I know, all new cars from 1/9/15 must meet Euro 6. So, I think there will be significant wriggle room to negotiate a deal especially if you find a dealer with stock to dispose of. Only a few days before these cars have to be registered and then they'll lose about £1000 in value. I reckon you might get a deal by phoning around and then visiting the most likely prospect.
In that case it may be worth waiting until early next month after they have been pre-registered? I've been in touch with half a dozen dealers now and they are all quoting the same price +/- £100.