It was not a term many people used four years ago, but "fake news" is now seen as one of the greatest threats to democracy, free debate and the Western order.

As well as being a favourite term of Donald Trump, it was also named 2017's word of the year, raising tensions between nations, and may lead to regulation of social media.

So great is the danger, the “Doomsday Clock”, which symbolises the threat of global annihilation, remains at two minutes to midnight thanks to the rise of fake news and information warfare, its keepers have said.

In a major report into disinformation and fake news, the Digital, Culture, Media and Sport Committee said electoral law was "not fit for purpose" and should be updated to reflect the move to "microtargeted" online political campaigning.

And yet, nobody can agree on what it is, the extent of the problem, and what to do about it. Here's everything you need to know.

The origins of fake news

Governments and powerful individuals have used information as a weapon for millennia, to boost their support and quash dissidence.

Octavian famously used a campaign of disinformation to aid his victory over Marc Antony in the final war of the Roman Republic. In its aftermath, he changed his name to Augustus, and dispatched a flattering and youthful image of himself throughout the Empire, maintaining its use in his old age.