He's in his 50s and doing coke and E? Was he a late starter? Friends and I did that in our 20's and even early 30s. Not when married with children.
You have a right to divorce him for unreasonable behaviour. Drink/drugs are one of the things listed in the first few lines of 'unreasonable behaviour'.
Seek legal advice, do not tell him about it. Just see a solicitor now. Do not discuss.
My husband was 'party boy', hell I was a party girl. The children came along and there is not even a cigarette smoked in this house. Believe me, we were caners! We've had our fun, fun doesn't start at 50 fgs.
You can't kick him out, but you can seek a divorce. I'm very liberal when it comes to drugs but I would not be tolerating that. It's abuse, emotional/mental or whatever they will call it. Get rid of him. How old are your children? This is not acceptable.
Even if your children are over 18 and you have to sell the family home I'd rather do that than live with him. Has he got a pension, you are entitled to a percentage. Seriously get legal advice ASAP.
Oh, and he's locking himself in the spare room it's for an extra toot for sure. This is not a LTB case, it's a kick the arsehole out of your home via the law case! Get a good solicitor, get yourself well armed and get rid.