Not me, my colleague. Utterly deserved, harsh as that sounds. My concern is whether I will have to give any 'evidence' during the capability process -are other staff involved at all? It's a horrible situation.
You shouldn't be involved unless you are given the task of providing specific support in order for the teacher to meet specific targets. Even then, you shouldn't be informed that the support required is within the capability procedures. If you are the supporter, you shouldn't then be part of the assessment process.
For example, if lack of progress in maths is a key issue, if you are the maths co-ord or key phase leader, then you could be directed to support maths planning, team teach, provide model lessons etc. But you should not be the person who then observes the colleague after the support package to assess if capability procedures can be stopped.
You should only be asked to support a colleague during capability if the area you are supporting is within your actual job description. If you are say HoD for Humanities, you wouldn't be expected to support a science teacher with subject knowledge.
IME when it comes to capability, steer well clear of all involved. And do not get involved in discussions with SLT where they are probing your "opinions" of your colleague.