In my D/O the indoor duties were 1 in 4 for about 10 years. The delivery duties were 1 in 6.
The idea was that the 1 in 4 was a kind of sweetener for working full hours every day.
After the revision our DOm told the indoor duties that they would have to work 1 in 6.
This was taken to a level 3 grievance and the outcome was that it had been agreed with the Union and signed off.
We asked for a copy of this agreement as our local and area reps denied signing this off, but we have never seen it and never will, we just have to work the 1in 6 and have done for about 8 months now.
As somebody has already said, they will put through whatever they want and no matter what agreements it breaks there isn;t a thing you can do about it, because they will roll out bullshit after bullshit to cover it all up.