One of the issues with Class 222 Meridians as I remember, was that a 'panic button' was provided in the buffet in case a Custoner Host was being attacked or robbed etc. This was basically a variation on the 'call for aid' in disabled areas/toilets.
Call for aids only sounded in the saloon, for the Train Manager to deal with, not the Driver's cab (which I believe happened on Voyagers - MML Driver's reps objected to 'call for aids' sounding in cabs as being a distraction, so only a passcomm would sound in a cab).
This could lead to the scenario of a Customer Host in the leading set being attacked and pressing the 'panic button', the Train Manger in the rear set responding, but then being unable to contact the driver until the panic button was reset (which wouldn't be a priority of the Customer Host being attacked). The train would in the meantime be continuing on it's merry way...
So a second Train Manager was argued for, for the front set.
If that's right, what I remember being told at the time, then the design and specification of the units was the underlying issue, and also explains a little why Voyagers weren't subject to the same industrial relations problems and resolutions.
In the future, RMT members will quite possibly be going to be subjected to redundancies when Hitachi trains arrive (if their communications handsets are set up differently), as the company can argue a second Train Manager isn't needed.
A completely unstaffed unit on EMR doesn't currently happen, but if it came in on 12 car 360s, then the company can play the 'precedent has been set' card, and RMT member's jobs will be definitely under threat.
The RMT are trying to protect their jobs, sometimes people win when that happens by the employer making concessions, sometimes (like Gatemen on the tube when sliding doors came along, and then the second, front Guard, on the tube, when the 'louaphone' communication with the Driver came along) it doesn't.