Friedrich Merz, the conservative frontrunner in the German election, is focusing his campaign on proposals to revive the struggling economy after a bruising clash last week over tougher immigration rules.

Former German Chancellor Angela Merkel has issued rare public criticism of her successor as the country’s center-right leader, the front-runner in Germany’s election next month, for putting to parliament proposals for tough new migration rules that only passed with the help of a far-right party.