"to get productivity growing again, labour has to become more expensive" Productivity is the saleable value of the work, not the cost of the work. The latter

"to get productivity growing again, labour has to become more expensive" Productivity is the saleable value of the work, not the cost of the work. The latter is only a floor for the former (since work that cannot be sold at least at its cost will simply not be done - witness the rise of fast food robots).