Thanks very much for your advice black_jack. I took it to another garage and they and a bodywork firm next door say they could not see any signs of a fault and it looked oiled. In addition the safety catch and lock are still working even in the bonnet's current bent state. I'm waiting for the insurers to get back to me as to whether they consider the accident caused by the MOT garage [claimable] or wear and tear [not claimable]. The MOT garage deny any wrongdoing and the insurers do not seem to be interested in claiming off that garage. But I suppose the MOT garage could always say that there's no way of proving that I didn't open the bonnet and close it improperly after the MOT.