A 62-year-old former rival of Angela Merkel who retired from politics nine years ago has emerged as an unlikely early frontrunner to succeed her as leader of Germany’s Christian Democrat party (CDU).

Friedrich Merz is the most popular candidate for the party leadership with ordinary voters, according to two rival polls published on Wednesday.

The surprising results put him ahead of Annegret Kramp-Karrenbauer, the current party chairman who is thought to be Mrs Merkel’s preferred successor, and Jens Spahn, the health minister and darling of the right-wing.

They will make troubling reading for Mrs Merkel, who announced this week she will step down as party leader in December but wants to stay on as chancellor until 2021.

There is no love lost between her and Mr Merz, whose political career stalled after he lost a power struggle with her in 2002, and she may find it difficult to forge a working relationship with him as party leader.