In September my wife had the catalytic converter replaced on her car at Kwik Fit, we are now onto our 4th replacement after the previous ones were all faulty, the CAT currently on the car has again become damaged and we are waiting on Kwik Fit getting a new part, we have been waiting over a week for this to appear.
What effect can a damaged catalytic converter have on the rest of the engine?
Not sure what you mean by "damaged"...but if a CAT is faulty, the only thing that suffers is the quality of the emissions...the engine won't be affected.
Don't forget, that CAT belongs to you.Because of its high scrap value it should have been returned to you to take to a scrap yard or you should have received a discount on any cost incurred.