As his employer you have an obligation to protect him in the workplace, even if that means protecting him from himself.
I would issue a formal letter to him, stating that due to health and safety issues it is now company policy to have 'no alcohol policy. If you have any suspicion that he has been on the booze the night before, ie you can smell it / sense from his actions that he is not with it, then remove him from the workplace without pay (this falls under the 'unfit for work category).
Before removing him from the workplace, confront him politely and inform him that (for whatever reason) you believe that he is under the influence of alcohol in the workplace. If he says yes, then remove him. The next day issue a letter stating that he was removed from the workplace for health and safety reasons, - ie under the influence of alcohol in the workplace, and keep a copy.
When it happens again, remove him again and issue another letter the next day explaining that this is the second occurance and that any further instances will not be tolerated, and will be considered to be gross misconduct. (keep a copy again).
When it happens again, hes fired, without a leg to stand on, and by the sounds of it righty so as this guy is a bad accidnet waiting to happen, just not to himself, but to the public, yourself, and peoples property.
Grant.