The single biggest known British political advertiser on Facebook is a mysterious pro-Brexit campaign group pushing for a no-deal exit from the EU. The revelation about Britain’s Future, which has never disclosed the source of its funding or organisational structure, has raised concerns about the influence of “dark money” in British politics.

The little-known campaign group has spent more than £340,000 on Facebook adverts backing a hard Brexit since the social network began publishing lists of political advertisers last October, making it a bigger spender than every UK political party and the government combined.