The lesson to be learned by companies is to take documentary proof (the insurance certificate) from the person hiring before they drive the car away. Otherwise the company will face a no insurance summons (for not checking).
The lesson to be learnt by an individual is always to make sure you are insured on any vehicle to be hired. Check with documentation before you drive the car away. Otherwise you can face a no insurance summons.
It was reported yesterday in the local media that a high value sports car that was parked outside a police station was impounded and the hirer and the hire company to be taken to court. The Lamborghini with a value of £180,000 is to be sold off and the proceeds to be kept by the police if no one claims it within 14 days it has been reported. Full story can be found here: http://www.bbc.co.uk/news/uk-england-cambridgeshire-33861563