Having your car keys on your person whilst drunk is not an offence. There is no such offence as intending to operate a motor vehicle whilst under the influence. The only offence he could have been charged with is drunk in charge of a motor vehicle and for that he would have had to have been observed driving the vehicle or been seen, sat behind the steering wheel of a vehicle with the keys in his possession. Otherwise it would be illegal for any campervan driver to have a drink and then sleep in the vehicle. Also if you are in the back seat or rear of a vehicle you can't be done no matter how drunk you are.