Imagine I'm a passenger visiting my parents in York. I work in Farnborough and I have to be in work on 27th because I can't get the time off. I don't drive a car.
Now I would be happy to travel back on the 26th using an off peak ticket but as no trains run to Farnborough on the 26th I end up travelling in the peak on the 27th. In addition to that I get caned for extra cash because peak restrictions apply.
If peak restrictions didn't apply then it would be better.
That's just an example. I've not checked what East Coast trains, if any, run on the 26th. Certainly no South West Trains services run to Farnborough.
I'm not saying they must do. Just that it would be good if they could relax the restrictions on the morning of the 27th.
They could relax the restrictions for the whole week twixt Christmas and New Year, whilst 27th onwards is 'normal' working, most places shut down for the week, as they know a majority would simply go sick.
So peak travel would or is at a far reduced rate, but no doubt they would say it would see too many travelling !
More services are creeping in on the 26th, but it does seem a very slow rate of increase, as far as most railway workers are concerned, if you are booked off all well and good, but if its not your rest day, and are booked to work the 26th, which over 60% / 70% of Signallers are, then so be it.