Can someone please give me the best website / phone number / organisation to go to for fathers who have had a relationship breakdown & are facing custody issues?

BIL has been staying with us since January, he has a 7mth old son & today his MIL has threatened to apply for custody of his son, calling both him & SIL bad parents & saying he will never see his son again, unless he continues to pay half SIL's rent each week.

Now I know most of that is codswallop, but he really, really needs legal advice.

He says he has called Legal Aid & they told him they don't deal with it, & told him to call somewhere else, he was a bit hazy on who exactly....

So what's his best next step?

Thanks in advance.