Actually, it gets even worse.
So, he stayed at his friend's house for the night. But then at about 6:30AM, she phones my mum to say he's upped and left, and she can't find the knife he came in with. Then we hear him knocking at the door.
My mum's first instinct had been to phone the police as soon as she heard he'd left, and they were in attendance within minutes. We thought he'd left because the knocking had stopped, but the police quickly found him hiding behind an alcove in the garden. They couldn't find the knife (he'd either disposed of it or just not taken it with him and his friend had simply lost it) but he was clearly very unhappy about being kept out of the house. He was detained by the police, given his mobile phone and a few other belongings he was ranting about, taken back to his friend's house, and told not to come back here today.
So now we're going to head down to the Citizen's Advice Bureau to get advice on obtaining a formal separation and getting things so he can't come back. Of course now he's got his mobile phone back, he's using that to phone us. Obviously the kicking him out and calling the police on him aren't strong enough signs that he doesn't have a home here any more.
Edit: OK, further minor stuff.
Citizen's Advice Bureau, closed. Lack of staff. We'll try again on Friday.
I forgot to mention when my dad had the knife and was talking to grandma, it seemed pretty clear he was threatening to take his own life. He said he'd rather kill himself than go to the Moorlands Housing Association, pulled the knife out, and said "What do you think this is for?". Crazy stuff.
Also, I think I may have underestimated his intelligence. We checked the kitchen knifes and none were gone, but we forgot to check the dining room steak knifes. Turns out he took one of those. He also did bring the knife to this house, but blabbed to his friend that he stashed the knife in one of our plant pots. We found it, and have informed the police, who should be paying closer attention to him now since when asked he actually denied ever having a knife, saying both grandma lied about seeing it and his friend lied about taking it off him.
He's currently down one of the local pubs, probably scrounging some more drinks. Tonight will be interesting, the police may be needed again.
Edit 2: Things may finally be calming down. A police officer arrived to take the knife as evidence, and noted that the whole police station knows about him now, and she's going out to patrol the town centre so she may end up seeing him at his favourite pubs, The Valiant or The Bird in Hand. She said if he comes back to the house, we should just dial 999 and get the police out. If nothing else, they'll arrest him for disturbing the peace if he comes back again, since he's had enough warnings to stay away.
Edit 3: Right...
Got a call from dad. Very apologetic, very pleading, very looking for sympathy, and very looking for a way back into the house. Mum wasn't having any of it, hung up on him.
A while later, we get a call from him saying he's in the back of a police van being taken to a mental hospital. He implies this is our fault. We check with the police, they say after an unspecified incident they arrested him under a section of the Mental Health Act and transferred him to the Harplands facility where he could be assessed.
Later still Harplands call us and we get the full story. The incident was dad leaning back off a bride at the edge of town threatening to throw himself off, and telling the police to stop the traffic below so he wouldn't hit any cars. More attention seeking. After his arrest and transfer, he agreed to voluntarily stay for the night. Harplands say if he wants to leave they'll have to assess his ability to make a rational decision. Even if they judge he's not capable of making one, they can only hold him involuntarily for 72 hours before they have to either release him or get the doctors to have him officially sectioned.
Bear in mind at this point that he's currently been drinking almost constantly for two days, has not changed his clothes, has not bathed, and has apparently not even eaten in that time. One can only hope that he looks at his situation and finally realizes he's got to sort out his life not for my sake or his wife's sake but for his own sake.