Wellington would not risk his army defending deep into Portugal unless the conditions were right. Instead he implemented a scorch earth policy to prevent the invading French from living off the land. He fought and defeated the French at Busaco on 27 September, but knew he could not stop them. Late on 28 September he ordered the army to continue its retreat. The officers and men of the Light Division reached Coimbra two days later after marching 36 km. They were surprised by that the Army’s Commissary Department was unable to evacuate all their stores. Tons of food and equipment was destroyed or left for the French. The next day they marched to Condeixa and found even more supplies. Lieutenant John Kincaid of the 95th Rifles noted that "the commissary officers handed out shoes and shirts to any one that would take them, and the streets were literally running ankle deep with rum, in which the soldiers were dipping their cups and helping themselves as they marched along."
Lieutenant James Fergusson of the 43rd also noticed the large amount of stores being destroyed, including cavalry equipments [sic], hospital supplies, tea, brandy, shirts, shoes, troswers [sic], and tobacco. . .”
The situation was the same in Pombal, 27 km further south. It too was another supply depot. Captain Leach of the 95th Rifles wrote that “So inveterate is the propensity of drink in the soldier, that, in spite of every precaution, many of them contrived to get drunk by dipping rum out of the streets, on our march through the town, in tin cups, or in any vessel nearest at hand.”
Lieutenant Henry Oglander of the 43rd Foot said that this neglect was deliberate on the part of the Commissary's part. "At Condexa considerable stores of liquor, salt provisions and tents were destroyed. The destruction and abandonment of stores is probably to be attributed not as the fault of the commander in chief, who cannot overlook the execution of every minute detail but to the ignorance and carelessness not say disinterest of the Commissariat. The later motive indeed I much fear had its weight, as any irregularity in their accounts may be easily concealed by adding the deficiencies caused by these scams to the list of articles destroyed already, which, I should think from the hurry and confusion inevitable in such circumstances, it would be next to impossible to discover."
My question is considering the retreat was planned for months why was the commissary department caught by surprise?