I have never expected any government to keep its word, least of all this one.
The fact that people do entirely different jobs does not preclude comparing them. That is why local councils are tied up in knots over giving extra pay to women employees as the result of comparing the pay of dustmen (a predominantly male occupation) and office cleaners (a predominantly female occupation until recently).
When I was at work we had a major job evaluation scheme using something called the 'Hayes Job Evaluation Scheme'. Everyone's job went through the mill, Research managers, senior engineering managers, cleaners, maintenance men, secretaries, the lot and we all came out with grades on a unified company grade and pay system. I admit it provided some very silly results and some specialities ended up with job specific bonuses to stop all the staff in that speciality resigning en-masse when they saw the pay that went with the grade, others were paid way over the odds but generally it worked.
Engine drivers are earning as much as airline pilots, who start at between £25 - £45k and an aircraft captain can earn as little as £54K. Please no one say their jobs cannot be compared.