Got it wrong, DP, that's a relief.
Do you have a drugs policy in your contracts? I would definitely consider him discussing drug use whilst at work, possibly by company email, hopefully going with the line you don't want to escalate it further, but you can't have an employee on the books who is so open about illegal activities. Also being abusive to a senior member of staff during working hours. Using company mobiles to do x/y/z, whilst not specified in the contract, it's not appropriate. I would also call the phone company and block him from running up a massive bill.
The main thing I would be concerned about is him trying to get revenge some how. So remove all his ordering capability. Stop any business related credit cards or debit cards. Get the manager to keep him on enhanced supervision, you don't want him ruining the livelihood of fellow members of staff because he has a vendetta. I don't know what the business is, or what it involves. Consider ways he could jeopardise the business, put in preventative measures. It might be advisable to put him on gardening leave from immediate effect, as him not being there is better for you and your staff than him being there. I believe you can cite that investigations are ongoing, you will contact him at a later date to discuss the matters. He is to hand over all work related property.
If you have CCTV then good, if not considering the likelihood for what might happen, consider a quick fix, so if anything happens you have recordings, plus it'll help for insurance purposes.
Speak to ACAS to see if the suspension on full pay is viable whilst matters are investigated. If he has an ounce of common sense, being paid not to work is better than him being at work.
If suspension on full pay is viable, put in a gagging clause where he is prohibited to talking about your businesses, yourself, family members, members of staff. Again check if you can do that reasonably.
I would also consider checking company finances, to ensure that everything is in order and stock input verses output matches up. A Coke habit can't be cheap, whilst you were together, has he done anything work wise considered inappropriate. Arrange a meeting with the manager to discuss this further so you get as much information as you can.
Also consider CCTV at home and any other premises you own. Even if it's something from Argos cheap. Keep all bases covered.
Check through phone records etc, if you don't have itemised billing, I believe you can request it from the phone companies. Just check for chargeable activity.
If he has access to a computer, go in at the weekend and check internet history, take copies and back up. For example if he's been doing none work related things during working hours. Check your internet history at home too.
The bigger file you have with misdemeanours, the better chance you have of being able to go for termination of contract, with no repercussions.
I know it's late on a Friday, but call ACAS as soon as you can. Check through everything. Sort out CCTV but don't install till he's left. Don't talk to him when he's near the computer etc as his first thoughts maybe clear history etc. Make sure the manager or another neutral member of staff preferably male is with you to witness what goes on. Record the conversation on your phone too.
Really hope you read this ASAP.
You might want to consider that he's not allowed to work in a similar industry for a set amount of time, with contacts he may have.
Good luck. This is all to protect your other employees more than anything. Plus yourself.
Maybe a good way of putting it, would be to say, I've decided to place you on paid leave for a period of 2 weeks/1 month. I'm not sure if you have to give a reason, if you can call it a gesture of good will, given recent circumstances.