Polls are open across Germany as the world’s third largest economy chooses a new leader to guide it through an era of febrile immigration debates and souring relations with Washington.

Alternative for Germany (AfD) is now on course to win 20.5% of the vote, according to latest projections - but there is no way Friedrich Merz will work with it because of a long-standing political taboo against working with the far right, known as a Brandmauer - a firewall.