UK & Social Services advice

I'm just after a bit of advice - long story short my SO's ex doesn't let him see him daughter and hasn't for 2 years. We are in the process of gathering evidence (and saving money) and starting court proceedings. We have tried to mutually sort it with her but with no avail. We often write letters to his daughter and post them - all lovely things and memories etc.

We recently found out that she's been telling others that social services are involved - that's why she doesn't let them see each other.

Surely, if that was the case he would know if social services were involved? Or can they be involved and advising her behind his back? Any advice is appreciated xx