Wow, that's a really tricky situation. I don't envy the position you're in.
It sounds like your so-called Dad is a complete w****r, it appears to me like if you took your £5k then it would be used as some kind of leverage back into your life. If you think you can deal with this and it would not have a detrimental effect on either your wellbeing or your relationship, then I think 5 grand is the very least that you deserve from your father.
However, if you feel that, in any way, you could be adversely affected by being reuinted with your Dad then I don't think it's worth the hassle.
I truly wish you all the best, with whatever you decide to do.