MIG wrote:

No announcement at any time on either occasion and I think a rather
disgraceful way to treat people.

I had a not dissimilar experience at Glasgow Queen Street, last year.
Services were disrupted and I arrived at QS at 18:15 on a weekday evening,
to find the station deserted (in terms of trains). I was heading for
Edinburgh Haymarket and wasn't in a desperate rush, so when the stock
finally arrived for the 18:15 train, I let it go, as it was chronically
overloaded.

The stock for the 18:30 train arrived (again late), a six-car class 170.
Passengers were allowed onto the platform and began to board both three-car
units. Just before departure, I was concerned that the PIS had not been set
and I began to wonder if the two sets were being split. At that point I
noticed that the door interlock had been engaged. I banged on the window to
the platform staff, once it became evident that the front cab of the rear
unit had been opened and that another member of staff was in the cab. There
were upwards of twenty people in the unit and I gestured to the platform
staff that they were all expecting the whole set to go to Edinburgh. There
had been no platform announcements and there were no on-train announcements
and there was nothing showing on the monitors to indicate that the front
three cars *only* would form the Edinburgh service. Eventually, the doors
were released and we were allowed to detrain, just at the point that the
doors were locked on the front three cars and the unit departed for
Edinburgh, leaving all of us to wait for the 18:45!

Again, there was total disinterest from the platform staff and the driving
staff, who had falsely imprisoned us and disrupted our journeys, and no
apologies for the incompetence and lack of information or warnings. The
three cars that we had been trapped in eventually formed an Aberdeen train.