I have just stumbled accross this particular peice of advice.
4.21 For example, the rate of interest charged under a credit agreement, or
the rate or amount of other fees or charges, may be so much higher than
those applicable generally in the particular market sector, or payable by
borrowers in similar situations, as to make the relationship as a whole
unfair to the borrower. They may also, in the particular circumstances,
be oppressive or exploitive of the individual borrower even if they are in
line with rates prevailing at the time in the particular sector.
It should not be too difficult to make the assertion that gaining an MB contribution, for PCP only is therefore not only unfair to those wishing to buy outright using a loan, but also to those wishing to buy outright with cash.
The term, MB contribution would come under the term Charges in the above statement, as to take out a HP/LOAN or other form of finance, not including PCP means that the borrower would be required to take a form of credit he would not naturally have choosen, with which to buy his car outright, but is also unable to take fair advantage of an available discount for the same product as any other borrower.
The same applies to cash purchasing.
You can therefore expect to receive the discount, no matter which way you decide to purchase your car.
To get this point across to a dealer, you simply need to show the full paid price for the car, when bought outright, at the end of any term. If the discounts relate to the credit proving to be cheaper than a cash purchase, in amount paid for ownership, then the dicsount that applies would be enough to bring the price together or it becomes unfair.
Same also applies to any hire purchase agreement.
office of fair trading writes these rules. I am sure there are more, but the basis is that its unfair to practice to encourage the consumer to take out a form of credit they would not normally have choosen.