On arrival at Falmouth, England, after a crossing under filthy conditions, Allen and the other prisoners were imprisoned in Pendennis Castle, Cornwall. At first his treatment was poor, but Allen wrote a letter, ostensibly to the Continental Congress, describing his conditions and suggesting that Congress treat the prisoners it held the same way. Unknown to Allen, British prisoners now included General Prescott, captured trying to escape from Montreal, and the letter came into the hands of the British cabinet. Also faced with opposition within the British establishment to the treatment of captives taken in North America, King George decreed that the men should be sent back to America and treated as prisoners of war.