"The courts stipulate how much maintenance has to be paid. The son of a friend of mine has fallen behind with his payments. He's self employed and struggling financially. "
So the father should look for more reliable income and support his child - cheap excuses
"His ex is remarried, has a well paid job and is not dependant on his payments yet has stopped him from seeing his children and a result, my friend cannot see her GC."
The financial and marital situation of the mother is irrelevant- child support is for the child, not the mother.
If there is a custody order and the mother is not fulfilling it, it is his right to go to court, so the gp can also see the gc
"My friend is not in a position to offer financial support. If parents in these situations want to be unreasonable there's little that can be done."
Yes, the father should step up and face reality
Another way traditional society vilifies the mother and leaves fathers off the hook
The King's Speech To Announce 'All But The End Of Leasehold System' System'


