All parties are fully comp (Direct Line). The relatives are with Sabre. Hmmm. I've got a feeling this will get costly and complicated...

Three weeks ago a *** fool broke into a relative's car, took the handbrake off and pushed it into my wife's car and also into mine. After much procrastination, and a visit from an independent investigator, the relative's insurer agreed to his claim and are currently fixing the car. However, today my wife and I both received a letter the insurance company telling us that because the thief was not identified, they were not "obliged to cover our losses" under the RTA. Needless to say, we're both bloomin furious and will be contacting a solicitor on Monday morning. Anyone any advice?