Google is allowing hundreds of companies to scan people’s Gmail accounts, read their emails and even share their data with other firms, the company has confirmed.

In a letter to US senators Susan Molinari, Google’s vice president for public policy in the Americas admitted that it lets app developers access the inboxes of millions of users – even though Google itself stopped looking in 2017.

In some cases human employees have manually read thousands of emails in order to help train AI systems which perform the same task.

The disclosure has uncomfortable echoes of last year’s Cambridge Analytica scandal, in which political consultants covertly harvested data from 87 million Facebook users through a third-party quiz app.

The letter, initially reported by the Wall Street Journal and seen by the Telegraph, also says that app developers can and do share the data with other companies – as long as Google believes their privacy policies make this clear enough.

“Developers may share data with third parties so long as they are transparent with the users about how they are using the data,” said Ms Molinari.