Passage: At its peak, Britain had approximately 25,000 troops stationed in Iceland, all but eliminating unemployment in Reykjavík and other strategically important places. In July 1941, the Althingi adopted the American–Icelandic defence agreement, passing responsibility for Iceland's defence to the United States. As many as 40,000 American soldiers were then stationed on the island, outnumbering the native population of adult men. (Iceland's total native population during the war was approximately 120,000.)

Question: What was the most troops Britain had in Iceland?
approximately 25,000 troops