I have just received this message from Cross Country Trains
Allow extra time at Birmingham New Street station
From Friday 21 November 2014, Network Rail will be implementing crowd control measures at Birmingham New Street station on Friday evenings and at weekends to prevent overcrowding on the platforms over the festive season. The measures will also be in place on Monday 22 and Tuesday 23 December.
During this time, you may be asked to wait a short while on the station concourse to allow platforms to clear during busy times.
If you're travelling from Birmingham New Street, or changing trains there, please allow extra time to catch your train.
It is as I thought would happen, There is no extra capacity on the platforms. All this work is so that they can hold the passengers on the concourse. We are still going to get overcrowding on the platforms meaning that they have to close access to the trains if there are too many passengers.