The grade naturally relates to the pay scale but as some jobs that some groups of MTOs do is more complex that others, the pay and hence the grade varies. Also hospitals in London (and I expect other large cities)who find it hard to recruit due to the high cost of living also tend to put people on higher grades. Why are all the perfusionists I know on MTO5 grade when they are not managers? It the fact that they can demand these high salaries due to shortages of staff? or is the job so complex they deserve them?
These guide-lines will necessarily be just that and not hard and fast rules. Market forces have taken over from an ideal national plan that was unworkable in reality.
Here is my rule of thumb (Diclaimer! This is based on reality and experience and not official guidelines

):
MTO2 needs to be supervised and trained
MTO3 can work alone on routine tasks
MTO4 works on more complex tasks where there is no background and uses experience and knowledge
MTO5 manages the section/department
I have not employed an MTO1 in a Central London hospital, no-one will or can afford to work for that wage. This is one of the problems of a national set pay scale.
Robert