“However, closer examination of the audit certificates published by the Audit Bureau of Circulations Electronic reveal that the site switched its internal measurement tool between February and March this year, ditching HBX SiteCatalyst in favour of WebTrends 7,” the Guardian stated.

The site has also been under-reporting traffic data for awhile, because some pages were not being tracked, the Guardian reported, citing a source.

Richard Foan, managing director at ABCe, told the Guardian that a publisher runs the risk of under-reporting traffic figures if it doesn't tag all the pages on its site. However, Foan would not comment on the Telegraph's audit.

However, Edward Roussel, digital editor for the Telegraph Media Group, told the Guardian that switching systems did not have anything to do with the large increase in user numbers, as both systems use the same methodology.

“There was leakage on both systems because we weren't able to tag everything with WebTrends during March,” he said, according to the Guardian. “This was minor leakage of less than 2 percent, or a few thousand unique users, so this was not a significant factor, or even a factor at all.”