Like Ranolki, I can find no evidence that a DLI battalion was stationed in the Channel Islands during WW1. According to Wikipedia
"In 1914, the British garrison was withdrawn at the start of the First World War and the militia were mobilised. Jersey men served in the British and French armed forces. Numbers of German prisoners of war were interned in Jersey."
However, since there were German PoWs housed on the islands, there would also have been a military guard force, which might well have been made up from units designated for the defence of the UK mainland. I think it unlikely, for political reasons, that the British would have asked the French to carry out the task.
While Patsy may have joined the DLI, that doesn't mean that he would have stayed in the same Regiment throughout the war. Many of the DLI's 40 odd battalions were just cadres and so he might have been transferred to another Regiment which was forming a new battalion at the time, and gone with them to Guernsey.
Since the
Visit Guernsey website invites questions about (among other things) its history, perhaps you could ask them your question.
