I have just had a nasty experience. Two men who had done a small roof repair job on my house while I was doing a bit of routine stuff on the van. They wanted more work, but I declined. They left and when I raised the bonnet, which had been down but not latched, I saw the oil filler cap was missing. Looking inside I saw something, which turned out to be a fistful of cement mortar mix. My question is, would insurance company cover damage to the engine if, despite my best efforts, I have not removed every speck of sand and the engine is ruined? Or, do I not tell them until after it goes wrong, pretending I knew nothing about it? Third, do I just start it and hope for the best? I will not employ people who 'just happened to be doing a job up the road'.