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FutureLearn says it has 370,000 students enrolled for a British Council course preparing for an English language test.
|Photo: BBC News|
This so-called Mooc - a "massive open online course" - has its biggest audience in the Middle East.
Simon Nelson, FutureLearn's chief executive said it showed the demand for English and scale of online learning.
There is an "enormous market" for learning English, said Mr Nelson, who predicted there would be even bigger numbers for such online courses.
FutureLearn's course, aimed at students preparing for the English language proficiency test IELTS, has more students than a course previously claimed as the biggest, a social psychology course from Wesleyan University in the US, which had 260,000 student.
Mr Nelson said that online learning was not only about a "volume game", but the figures showed what was possible when courses were available "unimpeded by geography".
The six-week course, Understanding IELTS: Techniques for English Language Tests, has students from 153 countries, with the biggest number from the Middle East, Asia and Latin America.
The most typical profile for a student was a young woman in full-time work.
Source: BBC News