Joseph Afrane, a campaigner in favour of Brexit, makes his point outside parliament yesterday — the day that Britain had been due to leave the European Union

Jeremy Corbyn and Boris Johnson face an effective ban on directly campaigning for their candidates in key marginal seats under new rules that will change the face of British elections.

Following a Supreme Court ruling, political parties have been warned by the Electoral Commission that they will need to apply strict spending limits to national campaigns that boost the prospects of local candidates.

The rules will curtail the freedom of political parties to target voters in key constituencies using social media advertising. Party headquarters will also be prevented from parachuting in campaigners to “must-win” seats in the way that helped the Tories to win the ground war with Labour in the 2015 general election.

The ruling came in relation to a court case earlier this