Composed (I think) by Atos, although approved and owned by DWP, which is why it is held on their website.
This is THE reference manual for Atos HCPs with regard to the WCA. You may not agree with all of its contents and principles, but it does at least define some very clear standards that HCPs must follow even though many do not, which can obviously then form part of a valid complaint.
It also shows where questions asked at interview are "loaded" - i.e. the answer to a seemingly innocent and innocuous question is interpreted with a very precise meaning with the inherent assumptions being totally overlooked.