When we haven't seen or spoken to each other in years?
I'll try and make this short and sweet.
We've never had a proper relationship. My mum divorced him when I was 5. He was awful, abusive and a cheating alcoholic. Never touched me but I have blurred memories of him abusing my mum. He was married before he met my mum and had 3 kids from that relationship, never bothered with them either and if he did it was only because my mum encouraged him to. I know it was a difficult divorce which cost my mum thousands just because he was awkward and nasty. He owns his own company and has done for the last 25+ years. When my mum took him to court for maintenance he lied and said he was unemployed. He was able to get away with it because he made my grandma (his mother) the director of his company. She was 73 and he owned a building company 
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Anyway, eventually my mum did win in court and he had to pay out, not very much that I'm aware of but by that point she had to use the money to pay off the court fee's etc.
After that he was granted excess and was suppose to have me every other weekend. He would pick me up on a Friday after school, drop me off at my grandmas and then pick me back up on a Sunday morning and take me home (whilst pretending he'd had me all weekend when really he was probably in the pub or out shagging about as usual). Over the years our contact decreased. As I grew up I realised how much of a manipulative arsehole he really was and decided to cut all contact, as did my other siblings. My mum pretty much raised me all on her own by working a full time job. Over the years he sent me random cheques in the post, £200 here or £50 there. Not that it ever amounted to what he'd actually have to pay if he'd been a decent father. I took the money, said thank you but we never reconciled. There was always a catch 22 when he sent money though. He would always text me afterwards asking if we could meet up or go for lunch etc. One year he asked me to spend Boxing Day with him instead of my mum and family (who have brought me up and always been there for me) I said no of course. No idea why he thought I'd agree in the first place 
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Now he's in 60's and I'm 25 working full time. Have been renting for years but desperate to get on the property ladder but it's just so expensive. I've saved and saved for a long time but need more to even be excepted. My mum doesn't have any money and I wouldn't want her to go into debt to help me. I'm sure she would though. Step dad will happen but I'd have to pay it all back of course. My dad still owns his company, lives in a nice house in a gated community, nice cars etc.. you get the picture. He's got a few quid in the bank. I've not spoken to him in around 7 years now and if I did get in touch it would only be for money. I would make that very clear if he asked what my motives were: I have no issues with it and I believe it's his fault that's why things are the way they are anyway. I know my other siblings have recently reconnected with him, one of them even started working his company but I know it's only because they want his money. AIBU to ask him for financial help towards buying a property? Since he's done sweet FA for me my whole life anyway. The worst he can do is say no and I would make it clear that we will never have a relationship, I just want the money so if he sees his arse after that then fine. I will survive without him like I always have.
My mum is also a bit upset that she can't help me more and doesn't want him to think I'm desperate for his money. I've never needed it before so why now. Personally I don't give a shit what he thinks.