I have had a reply and although they have apologised I want to know what they are going to do to make sure it doesn't happen again.
I don't want to sound pushy mother BUT I feel their systems for dietary needs are a bit rubbish (I think they resort to memory!).
Ok reply was...
We use cadburys and tesco value, will check on Monday which is open at the moment. If it is due to this then obviously we offer our deepest appologies. Staff do check for any allergies/ dietry requirements for individual children. I made the hot chocolate on Friday so if it was value hot chocolate and if it does contain wheat then it is my fault. I am sorry to hear that DS has been been unwell and i hope that he is better now.
We are normally really hot on things like this, especially on DS's requirements with wheat. DS and DD are normally very good too.''
Its irrelevant which hot chocolate they used as they BOTH contain wheat/gluten are unsuitable for coeliac/wheat/gluten intolerance!!
Any advice, thank you?