17:08 Portsmouth Harbour to Cardiff Central due 20:38
This train will be started from Fratton.It will no longer call at: Portsmouth Harbour and Portsmouth & Southsea.This train will run short formed with 1 carriages.This is due to a member of train crew being unavailable.
I believe it, but how on earth does a lack of a member of train crew reduce a 158 down to a 153?
I bet you it's this:
The train crew was late for that train, hence causing a knock on effect down the line, and therefore it had to reverse at Fratton. In addition, I betcha the train crew who took it down there was over hours and the replacement crew couldn't make it down to Portsmouth Harbour in time.
In addition, it's a 153 because it's First Great Useless.