The move follows reports that ministers, including former health secretary Matt Hancock, used private email accounts for government business.

Hancock resigned for breaching social distancing rules during an affair with an aide.

The ICO will investigate whether private correspondence channels were used, and if their use led to breaches of freedom of information or data protection law. The regulator has served information notices on the department and others to preserve evidence.

Information commissioner, Elizabeth Denham, said in a blog post: “The suggestion of ministers and senior officials using private correspondence channels, such as private email accounts, to conduct sensitive official business is a concerning one. It concerns the public to feel there may be a loss of transparency about decisions affecting them and their loved ones. And as the regulator of data protection and freedom of information laws, it concerns me.”

While the use of private communication channels does not break freedom of information or data protection rules, Denham added: “My worry is that information in private email accounts or messaging services is forgotten, overlooked, autodeleted or otherwise not available when a freedom of information request is later made. This frustrates the freedom of information process, and puts at risk the preservation of official records of decision making.”

There are also concerns that emails containing personal details are not properly secured in private email accounts, she said.

The government’s Code of Practice sets standards for ministers, including the importance of good records management, while the ICO has previously set out guidance on the use of private communication channels.