A paper I was reading made reference to an island called Lerne saying that it was north of Britain, but I cannot find out what island it is referring to through google, nor does the paper make mention of it again.
I believe you or the author has made a mistake in the spelling. The all-mighty Hornblower et al. Oxford Classical Dictionary doesn't have an entry on 'Lerne', and a Pleiades (an online database for ancient place names) search does not yield anything. There's an area better known as 'Lerna' in Argos, Greece that Strabo in his Geography mistakingly calls Lerne, but obviously it's nowhere near Britain. My best guess is that the article is actually referring to Ierne which is an ancient name for Ireland, but of course it's rather weird if this wasn't specified in the article. If you want to give more context, or just the exact quote and the article name, I might be able to mage a better suggestion if Ireland doesn't look like a realistic option?