Legal fees for fathers fighting to see their children can run into the tens of thousands of pounds. Regardless of what you earn if you can not afford this or simply do not have the money you can’t fight to see your own children. There are many fathers in the Uk today who’s only option is simply don’t see your own children. Spend years with no idea what they look like or how they are doing at school wondering every single day if they are ok. 
Mental health - I can only speak from personal experience not seeing my children is destroying my mental health as I’m sure it is others. I have spoken to many fathers who have told me of depression and suicide attempts that they have suffered because of the loss. 
There many studies available to view online about the effects of these situations on children themselves and none of them are positive.  
When a family member or friend dies they disappear from your lives completely and you grieve and are given support from those around you and your employers, NHS and other Organizations. 
I wake up every morning and have to grieve the loss of children I can’t see but the only thing holding me back is the inability to pay for help.   The minute a dad does not pay for his children he is hunted down and made to pay by the  Child maintenance service. If a Mum takes the children and refuses access nothing is done.