Dear all
Thanks for all the advice.
One of my chums in the Midlands says that New Street's long history of short-notice platform changes – which dates back at least to the 1970s-80s when I used it every day – is now consigned to, er, the history books. He's not a rail insider, just a frequent traveller through BHM, and says:
I’ve had a few recently that haven’t been announced officially - they’ve just been shouted by the dispatcher, along with a garbled tannoy that I could not understand.