The WRc grading runs from 1 to 5. Grade 1 defects are cosmetic and need no action; Grade 4 and 5 are structural failures requiring repair. Most Victorian clay systems show a spread — open joints, some root ingress, occasional serious defects.
The distances matter: they let a repair be located from the surface without exploratory digging, which is what keeps a patch repair cheap.
A good report is written in plain English with a summary at the front. If yours is a wall of codes with no interpretation, ask the contractor to explain each item before agreeing any work.