Leaving that aside, it's not a very interesting aspect of this discussion, the case hinges on the judgement of the social workers and that of the psychiatrist.
Is is it possible they could have made mistakes? Yes. I don't know whether they have or not, but it's not impossible.
I don't think that the bad press social workers sometimes get is fair, at the same time I don't think the training is adequate. In Germany for example, SW are in a par with psychotherapists in terms of training, pay and status.
There are cases where sws have made major errors of judgment, some of which are sadly famous.
The psychiatrist has to make a judgement as to whether one parent or another is telling the truth. And he has to make a judgement as to whether something happened for which there is no direct evidence. It comes down to his impression and his opinion.
Ms Dinnock would not 'accept' that her allegations about her ex were not true. That may be because she's an unrepentant liar, or because she believes them to be true. There is no hard evidence either way.
There are cases such as the shaken baby cases where expert witnesses have been wrong. In this case there's not even any physical data to go on.