It is alleged that MI5 created a ‘fake-off’ mode that meant television users thought sets were switched off. In fact users can be secretly recorded by them and conversations transmitted to a CIA operative listening in. The smart televisions come with a microphone that is normally used for voice-activated controls.

The leaked files also appeared to show evidence that GCHQ had collaborated with the CIA in hacking into Apple’s iPhones as well as smartphones run using Google’s rival Android software. The phones can even take photographs when owners thought them switched off.

According to the documents, GCHQ, the Government’s listening agency based in Cheltenham, worked on six different methods for targeting the iOS operating system used on iPhones, iPods and iPads and one for spying on Android phones.

In total the CIA developed 14 applications targeting iPhones and 24 aimed at Android phone users.

In so doing, WikiLeaks claimed the CIA was able to circumvent encryption codes used in such messaging groups as WhatsApp.

The CIA is alleged to have exploited glitches in the technology that the original manufacturer or designer isn’t yet aware of - called ‘zero days’ - to hack into the devices.

Another document suggests the CIA’s cyber directorate is developing ways to infect control computer systems in cars and lorries.