It wasn't a SW who got a mentally ill woman pregnant every year on the dot like a clock when she clearly wasn't coping. With 3 under 4 and another on the way I'm shocked dear Daddy found the time to do his best to impregnate some other poor soul. There's a helluva lot more to fatherhood than just bumping uglies like a dog in heat.
He should be looking at his own behavior instead of blaming SS. He had parental responsibility and didn't do HIS part as those kids had been malnourished and neglected a long time. He could have queued at the foodbank & made the kids dinner instead of making them eat biscuits, spent the day at the social to get a crisis loan when the cot broke so they wouldn't have to sleep in a pushchair etc, etc.
He could even have worn a sock on it occasionally to prevent further pregancies until she could properly cope with raising their first baby after they were allowed to keep the child despite SS concerns. He could have watched the kid/s while she accessed the appropriate treatment/therapy programme for her MH problems. I'm 100% sure that's what most decent men would do.
If he suddenly found her impossible to live with (but not to knock up every year!) then he could have applied to the court for a residency order for the children himself. There's no evidence he even attempted to do this, (unlike the poor concerned father and MIL of Baby P!)
In my eyes the father is the scum of the earth, and NO right to point any fingers of blame at SS. (Even if SS did make a few mistakes of their own, they weren't the parents! They tried to remove the eldest child legally and failed, this may have made them wary of the amount of evidence needed for a second attempt).