Thank you Ladymuck for your kind response.
the problem is i had no way of knowing he underperformed until the results came out, he could've easily achived in maths way more than what he did. Very unfortunate, he spent good few minutes in the toilet and he used it in the break as well.
I'm hoping on compassionate ground he would be given another chance to prove his ability, the exam day just wasnt his day.
He certainly won't be able to resit the exam, if that is what you are hoping? Unfortunately, in presenting him for the exam, you were indicating that he was fit to take it; if he didn't tell you that there was a problem and you didn't notice that there was anything the matter at the time, then to be honest, it is unlikely to have been that significant a factor.
One course of action would be to name the school on your CAF anyway; your DS will be refused a place on the grounds of non-qualification, but you can appeal. You will have the opportunity to provide evidence of your DS's academic ability and to mention anything you feel is relevant as a mitigating factor. However, one has to say that in general only a small percentage of appeals are upheld.