You need to go to a refuge. You can do this one of two ways 1. Contact a domestic abuse organisation and they will organise it for you or 2. Get in contact with the refuges directly and ask if they have space.
Do not tell anyone, including your own children, what your plans are as that may put them and you in further danger.
You usually go to a refuge the same day if there is space but don't worry about taking anything if it will put you at risk. Everything can be replaced.
The refuge will not be in the area you are, they never put you in the same area as it's dangerous. If you are contacting refuges directly then choose one a good way away from where you are, where you have no links so he won't suspect you're there.
The refuge has support workers who can assist you in working out a longer term solution.
OP, you sound terrified, it comes across in your posts. I want you to take some deep breaths. Breath in through your nose and out through your mouth.
Once you start to put a plan in place, things will seem easier. I know this is hard but what's the alternative? It's time to go and you know that, you are not safe there and you have more chance in a refuge than you do there. You know that.
One step at a time OP. The hardest part is already over and that's deciding to go. You already have your documents in a bag. If you can get any necessary medication or prescriptions together such as inhalers then that's great.
Don't worry about opening accounts or anything like that, you can do that at the refuge. They will usually have toiletries so don't worry about those. They are fully furnished and come equipped with the essentials. They are at hidden locations so you can't be tracked down and you will be safe there. They can help you organise benefits and longer term housing.
If you organise a refuge through Women's Aid, they usually cover the train fare for you. Others probably won't do this but some do actually pick you up if necessary. Each refuge is different so ask them about transport if you don't have the cash, they'll advise you.