My abusive ex is blackmailing me into staying.

My abusive ex is blackmailing me to stop me leaving — what can I do? (UK)
I’m posting anonymously because I’m worried my ex may find this.
I’m trying to leave an abusive ex-partner, but I feel completely trapped because he is threatening to deliberately cause problems in my life if I leave or don’t do what he says.
He has threatened to:
Contact my employer and falsely accuse me of stealing in an attempt to get me fired.
Contact my landlord about something in my home that they aren’t currently aware of.
Try to take my pet away from me.
Tell my family that I have continued communicating with him, while making it look like I willingly wanted contact when I actually felt pressured and scared to leave him and he also threatened to tell people things about me or twist situations to make me look like the bad person.
There is also physical and emotional abuse involved. When I don’t do what he wants, he can become aggressive, destroy my belongings, wrecking my house and say extremely horrible things to me. He has also physically hurt me on occasions.
Today he deliberately burnt some of my belongings and damaged/ruined things that are sentimental to me. This is part of an ongoing pattern of intimidation and control.
I feel like every time I try to leave, he finds another thing to threaten me with. I’m scared of losing my job, my home, my pet and my family, and I’m also scared about what he might do if I actually leave.
I’m in the UK and I’m looking for practical advice from anyone who has experienced coercive control/domestic abuse, particularly regarding:
How to document threats and abuse safely.
What I should do if he contacts my employer.
What I can do to protect my pet.
How to deal with threats involving my landlord or family.
How to safely leave when I’m worried about retaliation.
I don’t want judgement about why I haven’t left already. I’m aware that leaving sounds simple from the outside, but I’m genuinely frightened of what could happen afterwards. Please help.