Getting the latest news on a British government reshuffle once meant waiting outside the prime minister's Downing Street office for ministers to emerge, and judging their fate by the look on their faces.

But in the age of social media, David Cameron unveiled a major shake-up of his cabinet on Tuesday through his two official Twitter accounts, which between them boast 3.4 million followers.

"I'll be reshuffling the Cabinet today. Watch this Twitter feed for the very latest. #Reshuffle," the premier announced overnight.

When his Conservative party was still in opposition in 2009, Cameron famously explained his reluctance to join Twitter, saying: "The instantness of it, I think - too many twits might make a twat."

But he is now firmly on board, and amid the swirling and often contradictory rumours in Westminster, @Number10gov and @David_Cameron became authoritative sources of information about who was in and who was out.

Government ministries routinely use Twitter and 461 of the 650 members of the House of Commons have accounts, with former foreign secretary William Hague one of the most enthusiastic users.

Hague would often tweet reaction to breaking news to his 240,000 followers well before an official statement arrived from the Foreign Office - to the occasional consternation of the staff in the press office.

Hague's replacement, former defence secretary Philip Hammond, has yet to set up an official account and a spokesman said it was "too early" to say how he would use social media.

True to form, Hague announced his resignation via @WilliamJHague on Monday night just as Cameron tweeted a message of thanks for his four years in the job.

Since then, there have been 260,000 tweets about the reshuffle, and 100,000 mentions of the term, according to an analysis by Twitter.

It is not the first time the prime minister has used social media in this way, having unveiled a previous reshuffle in September 2012 through a string of tweets.

Twitter also allowed those who had been promoted to crow about their new job, and those who were passed over to have the final word.

Former defence secretary Liam Fox had been widely tipped to return to the cabinet, but as speculation grew about his failure to be promoted, he tweeted a statement pointing out that he had been offered a job - but had turned it down.

Former climate change minister Greg Barker, meanwhile, gave thanks for the online support after he was shown the door.

"As we all know Twitter can be a cruel mistress at times but have been really moved & surprised by so many lovely messages. #ThankYou," he tweeted.