IT is known as Britain's listening post, operating secretly to detect threats against national security.

But now GCHQ has emerged from the shadows of cyber space to become the first of the country's spy agencies on Twitter.

Its debut post, sent at 11.02am today from the account @GCHQ, simply said: "Hello, world."

Twitter may be more than a decade old and firmly embedded in the lives of hundreds of millions, but joining the site represents a departure for an organisation whose ventures on to the public stage have traditionally been rare.

The move is the latest step in a drive towards greater transparency after the service came under intense scrutiny in the wake of revelations by Edward Snowden in 2013.

A GCHQ spokesman said: "We know that some will say we're joining the Twitter party slightly late but we're the first intelligence agency in the UK to do this and it's a big step for the organisation as we become more open about the work we do to keep Britain safe."

Andrew Pike, director of communications at GCHQ, added: "In joining social media, GCHQ can use its own voice to talk directly about the important work we do in keeping Britain safe."