I don't think woman's aid will help unless there is DV/Abuse going on... though please someone correct me if I'm wrong.
Speak to the CAB and find out what could happen if you just walk away WRT the rental etc on where you were.
Get all your stuff together and put it out of his reach.
Depending on ethnicity, the person this guy owes money to could be very dangerous indeed.
As far as I've heard the middle eastern ones generally specialise in dope, but other more general dealers are from elsewhere and as they deal in everything else are used to dealing with hard core dealers and addicts so don't take any shit. That said, arabs don't take bullshit well either.
How has he got into this debt, by not paying for stuff and just smoking it without selling it? The mark ups even at that level can be huge, so to be into £1500 of weed is an awful lot of stuff to have smoked.
He really IS a prize twat and this is a deal breaker and you have to do whatever it takes to keep him as far away from you and your DC as possible.
My feelings are that for the sake of your DC, you need to talk to the police. They could even take these people out of the game, which would be good for everyone.