There was a rule imposed a few years ago to try and stop the car manufacturers (Renault being the main culprits) from offering their dealers thousands of pounds per car to pre-register loads of cars to artificially boost their sales figures.
Now, if a dealer registers a car to itself and sells it within 3 months they can be fined to the value of any bonus they were paid by the manufacturer for registering it, which is why you don't see as many "brand new delivery mileage" cars at franchised dealerships as you used to.
The manufacturers found a way round this new rule though, as all they do now is sell the cars they want to register to car supermarkets, at the same massively discounted price. By registering them to the supermarket, rather than the dealers, they have found a loop-hole.