I was waiting at Leeds tonight for the Northern 1736 to Manchester Victoria from platform 12a. Around 1730 a TPE train arrived onto the platform. The announcement was obscured by the engine noise but 'platform 12A' and 'Manchester' were audible. I could see it was the wrong TOC but a number of passengers boarded the train, particularly since the display screen continued to state that the 1736 to Manchester Victoria was at the platform. Time passed and the TPE train remained there and the display screen continued to say it was the 1736. Eventually at 1735 there was an announcement that the 1736 was departing from 12C and the display screen changed to say that the 12A train was the 1752 to Manchester Piccadilly. Cue hordes of passengers running down the platform. OK, there may have been reasons for a late notice switch of platform for the TPE train, but why pick a platform which would not only now be blocked for 20 minutes, it would be sitting where a train to the same city but a different route was due to leave before it? Even if there was no alternative to using 12A, why leave the screen with the wrong train displayed and only correct the error one minute before the 1736 was due to depart? So much that could have been avoided..