PIP passporting and cancellation of student loans

Odd query this and probably not under the right topic, but there is a PIP connection. The DWP passporting sheet (toolkit) states that PIP is a qualifying benefit for cancellation of student loans.

However, on further investigation, the relevant reg., which appears to be s19 of the Education (Student Loans) (Repayment) Regulations 2009, also states ... ‘(b) the borrower receives a disability-related benefit and because of the disability is permanently unfit for work;’

Think this was the case with DLA too, Has anyone been down this route with anyone?

Struggling to get my head around the ‘permantly unfit for work’ bit. Who decides that in these stranfge days of ESA, etc.?

Recent letter from HCP required as per:

http://www.slc.co.uk/services/loan-repayment/loan-cancellation.aspx

Simple!!!