In Campbell v. Allstate Ins. Co. (1963) 60 Cal.2d 303, the trial court denied recovery to a third party based on the insured's breach of a policy provision requiring him to cooperate with the insurer in effecting settlement of claims or defending against suits. The California Supreme Court reversed, holding that breach of a cooperation clause in an insurance contract is only a valid defense where it is shown that the insurer was substantially prejudiced by the breach. (Id. at p. 305.)