HCP assessor having appropriate background

I have a client with mental health problems. Her PIP assessment was carried out by a physiotherapist and she scored zero points. I want to raise the point that assessments should be carried out by someone with the appropriate background, ie a physiotherapist is unlikely to be experience in mental health problems, but can’t find the guidance/case law, I’m sure I’ve read it before but now can’t find it. Can anyone help with that?

Thanks in advance.

[2015] AACR 23 (ST and GF v Secretary of State for Work and Pensions (ESA) [2014] UKUT 547 (AAC))

https://www.rightsnet.org.uk/?ACT=39&fid=2&aid=2028_AyUJbHOEQmaTvDwCghVM&board_id=1

Thanks Mike. That’s very helpful.