There is an old Hotel/Pub in Marble Arch, London...
....which used to have gallows adjacent. Prisoners were taken
to the gallows (after a fair trial of course) to be hung. The horse
drawn dray, carting the prisoner was accompanied by an armed
guard,
Who would stop the dray outside the pub and ask the prisoner if
he would like ''ONE LAST DRINK''.
If he said YES it was referred to as "ONE FOR THE ROAD"
If he declined, that prisoner was "ON THE WAGON"
So there you go...!!!