Russian hackers threatened to cause massive disruption to British government departments and TV broadcasters in the run-up to last year’s general election, security sources have revealed.

The “imminent threat” by Fancy Bears, a cyber-warfare group thought to be linked to the Russian state, was thwarted by GCHQ, the government’s eavesdropping agency.

The disclosure comes amid concerns that Russian hackers are attempting to disrupt the US presidential election. Last week DC Leaks, a Russian-linked website, hacked White House servers to obtain what appeared to be Michelle Obama’s passport.

According to British security officials, Fancy Bears, which is also known as APT28 or Sofacy, threatened to attack every Whitehall server, including the Home Office, Foreign Office and Ministry of Defence as well as all the main UK