They gave a warranty; the car is not fit for the road, therefore not fit for purpose. Yes, he has a valid claim.
The seller should repair or replace the car, or refund the money. Replacing a used car at that price level might not be a realistic option, but if the dealer offers a replacement and your friend wants to consider it, I am sure he will have a mechanic check it out.
Have your friend make his claim in writing, supported by a copy of the independent mechanic's report. Tell him it might take some time (I say that based on what you say about the way they have treated him so far).
The fact that the dealer is not a member of SIMI has no effect on anything.