see
dft.gov.uk/vosa/repository/M … 202011.pdf
what is the right pay for an external TM?
TC specifies (being available for) 8hours per week for <2 vehicle licence, bearing in mind nat min wage.
I don’t believe the NMW applies to “being available”. Any contract to employ an external TM would specify how many hours actual work and some arrangement (I can think of several) to compensate for being available - in or out of hours.
I certainly would expect to earn £15 an hour for the working hours. That equates to £30,000pa. If I was getting 3am calls for help from drivers then I would charge an appropriate rate for that as extra. Since the TM would probably be self employed anyway I guess he would just send a bill for his time in the same way as an accountant or IT specialist would.