LONDON — Pity British voters.

Not because they face a choice between two historically unpopular candidates for prime minister — the Conservative incumbent, Boris Johnson, and Labour’s leader, Jeremy Corbyn — on Dec. 12. Nor because they are being forced to trudge to polling stations for the third general election in five years, this time in the depths of the miserable British winter.

Pity British voters because they are being subjected to a barrage of distortion, dissembling and disinformation without precedent in the country’s history. Long sentimentalized as the home of “fair play,” Britain is now host to the virus of lies, deception and digital skulduggery that afflicts many other countries across the world.

In this as in other respects, Mr. Johnson — a serial liar who lost his first job as a journalist for inventing quotes — resembles President Trump. And Britain, whose election is breaking down under the pressure of manipulation, increasingly looks like the United States. Truth and falsehood have become malleable concepts. Anything goes.

Social media is the staging ground. During a recent TV debate between Mr. Johnson and Mr. Corbyn, the Conservative Party renamed its Twitter account factcheckUK, which it then used to push out partisan messages designed to look like independent verification.