Reuters/Berlin

Schroeder, the centre-left Social Democrat (SPD) chancellor from 1998 until Merkel defeated him in 2005, also said in an interview with Der Spiegel magazine that the conservative leader had failed to groom a successor.

“To govern you sometimes need to have the courage to take risks,” said the 69-year-old Schroeder. “If you only govern along the lines of ‘Wait and see which way the majority is headed’, that won’t work in the long run. Always following the mainstream is not political leadership.”

His comments echoed criticism of Merkel heard in Germany and parts of the eurozone during the bloc’s debt crisis.

Despite that, Merkel remains popular at home and abroad. She won a third term last year, only the third post-war German leader to do so.

The criticism from Schroeder, who just published a book called Klare Worte (Straight Talk) comes at an usual moment because his party just joined a grand coalition with Merkel’s conservatives in December.

A year ago when the SPD was still in opposition, Schroeder had praised Merkel for “leading with restraint” in Europe. But he has also criticised her for timidity on reforms.

Schroeder warned Merkel against staying in power too long.

He said he believed two four-year terms are enough for any German leader – even though he was running for a third term in 2005 when Merkel and her conservatives beat him and his SPD.

“The pressures of the office are immense,” Schroeder said, adding that on top of that “the media and the public just want to see a new face at some point”.

He said Merkel would have a hard time if she runs again for a fourth term in the next election set for 2017. He said Merkel would be well-advised to look for a successor in her party.

“But the conservatives don’t have anyone in sight,” he said, adding that one would-be successor, Defence Minister Ursula von der Leyen, still has to prove herself.