 That was the aid and encouragement the British gave to the Spanish to harass the French behind their lines which led them to squander most of the assets of their Iberian army in protecting the army's line of communications.This was a very cost effective move for the British, because it cost far less to aid Spanish insurgents than it did to equip and pay regular British army units to engage the same number of French troops.As the British army could be correspondingly smaller it was able to supply its troops by sea and land without having to live off the land as was the norm at the time.