If he has an email from the dealer confirming the car has runflat tyres, and the car does not have runflats, the dealer has misrepresented the car and needs to either fit the correct tyres at their expense, or refund part of the purchase price to allow your dad to fit the correct tyres.

Contact the MD at that branch of the dealer (not the salesman who sold the car, the MD) and tell them that unless they arrange to fit runflats of the correct spec at their expense (or refund to your dad the cost of fitting the correct tyres - get a quote for this) within 14 days, you will go ahead and do it yourself, then sue them for the costs via the Small Claims Court. Point out that the dealer said via email that the car had runflats, and it doesn't, which is clear misrepresentation.

Then put the same in a letter which you send by registered post to the MD at the dealer. Keep a copy of the letter and attach the post receipt to the letter. This is evidence that you use if you need to proceed to Small Claims.