Accounts that have not tweeted for a time will not be affected, but if it has not been accessed then they will be deleted. While Twitter has removed and deleted accounts in the past, this is the biggest scale of deletion yet.

The BBC said a Twitter spokesperson suggested the move would “improve credibility by removing dormant accounts from people's follower counts, something which may give a user an undue sense of importance.”

"As part of our commitment to serve the public conversation, we’re working to clean up inactive accounts to present more accurate, credible information people can trust across Twitter," the firm said.

"Part of this effort is encouraging people to actively log-in and use Twitter when they register an account, as stated in our inactive accounts policy.”

The below screenshot is an example of the emails dormant accounts have received warning of their removal on 11 December.

Image: BBC

Some people are seeing it as an opportunity to grab desirable usernames that were taken in the early days of Twitter by accounts that are now inactive – for example single Christian names, surnames, and single words. Twitter insists the move has nothing to do with freeing up available usernames.