The express from Euston being late was pretty standard, due to the disorganisation of the line with excessive wartime traffic. At least two of the trains involved, the troop special and the "Jellicoe" coal train, were extras specifically for war traffic, and the down express had run 300 miles through the night through all of this. It was so normal for the local, which should have left Carlisle after the express, to be crossed to the opposite road to let it pass that the day signalman's practice had developed to take advantage of it.
I was always surprised the local was sent off ahead, through, as there must have been connecting passengers from the overnight for it, whose connections were lost, and it can't have gained much ground out to Quintinshill, being shunted there, compared to following immediately behind from Carlisle.