From Post Office Scandal blog by Nick Wallis, 2018:
The National Federation of Subpostmasters, once an actual trade union, now described as an independent organisation, is anything but. It is wholly in the pocket and pay of the Post Office and it is contractually obliged not to do or say anything which could do anything “materially detrimental to the Post Office”.
I want to deal with this in detail because it has really been bugging me for some time. If ever there has been an organisation which has utterly failed its members, it is the NFSP.
https://www.postofficescandal.uk/newsletter/day-6-write-up-the-post-office-speaks/