I agree with Melchior, a salesman in a main dealership is always going to tell you the car you want is in really short supply because he can use this as the reason he can't offer you a discount - "we can sell everyone we get, so we don't need to discount".
As far as I'm aware car supermarkets like Motorprovider & Motorpoint only supply imports & it's important to check these are paralle/pan european imports (EU member countries) &
not grey imports. Otherwise you could be looking at different specs, components (which might be hard to replace), anti-corrosion protection, poor UK dealer back up, increased insurance costs & lower residuals when you come to sell. As Supermarket cars are generally sold from stock (rather than to order) there is a possibility that it's been sitting around for sometime since it was PDIed by it's supplying dealer and you will have lost this part of the 2 year warranty - you can buy a 3rd years warranty for around £250. Also make sure the price quoted is the on the road (OTR) price as I have heard that they sometimes charge extra for registration, plates & tax.
If you're looking to order a car to you own exact specification, I can personally recommend Euro Imports (
http://www.euroimports.co.uk/), who source their cars direct from dealers in Denmark - depending on spec these take from as little as 5 weeks to come through. Not only do they provide a first class personal service, but their cars represent a very good saving on UK list prices. For example, the typical price of a GTI 3dr, manual, in red with interlagos interior & cruise control is £17,995 OTR - no hidden extra costs whatsoever.
