Should I lend my car to my brother?

Every week a Guardian Money reader submits a question, and it's up to you to help him or her out – a selection of the best answers will appear in next Saturday's paper. Any answers? My hard-up brother and family are arriving from the US and staying with us. He's asked to borrow my car and insuring him will cost a fraction of hiring one. I know it's only a car, but I look after it. And if he crashes, it will cost me a fortune. What would you do?