Germany’s “firewall against the far-Right” could crumble after the frontrunner to win next month’s election said he could work with Alternative for Germany (AfD) to tighten immigration laws.

Friedrich Merz, the conservative Christian Democrat (CDU) leader, said on Friday that his party would try to push through tough motions on migration while in opposition with the help of AfD votes in parliament.

It marks a significant about-turn for Mr Merz, who has repeatedly vowed not to cooperate with the AfD and has long been a supporter of the “firewall”, which refers to mainstream parties pledging not to work with the AfD – viewed by some Germans as beyond the pale for allegedly playing down the crimes of Nazis.

The liberal Free Democratic party (FDP) also signalled it would be open to voting with AfD for the CDU’s proposals.

Wolfgang Kubicki, FDP vice-chairman, said: “I don’t care who else agrees. We cannot link our approval of measures necessary for the country to who votes for us.”

Christopher Mayer, an FDP MP, said he would be “open to agreeing with the CDU’s proposals … let’s wait and see what they actually present”.