BERLIN (Reuters) - Germany and Europe would both suffer if the Social Democrats (SPD) vote ‘no’ in a ballot on a coalition with Chancellor Angela Merkel’s conservatives, a senior party official said.

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The SPD’s 464,000 members have been voting in a postal ballot on whether to endorse their party leadership’s decision to renew for another four years the ‘grand coalition’ with Merkel’s conservative bloc that took office in 2013. The result is due on Sunday.

Stephan Weil, SPD premier of the state of Lower Saxony, said during his last visit to Brussels everyone he had spoken to was adamant Germany should not drift into uncertainty.

“It would be bad for Europe, Germany and the SPD. There would be a period of political uncertainty,” he said.

French President Emmanuel Macron is keen to push ahead with reforms to the euro zone, but without a German government in place soon the window of opportunity to inject fresh dynamism into the European project will quickly close for this year.

Asked in an interview with daily Die Welt if an SPD ‘no’ vote would result in a national crisis, Weil said: “No, I wouldn’t go that far, but many people’s confidence in our political system would erode even further.”

The SPD’s Jusos youth wing has been lobbying party members to vote against a re-run of the grand coalition, arguing they would do better to rebuild in opposition after suffering a battering in last September’s election.

Weil conceded that if he were a Jusos member he would think about voting ‘no’, but decades of party membership had convinced him the SPD should solve its problems itself rather than use them as a reason not to take part in government.

Merkel’s conservatives entered into coalition talks with the SPD this year after talks with two smaller parties on a three-way tie-up collapsed in November.

Jens Spahn, a member of Merkel’s Christian Democrats (CDU) who has been critical of her at times, said the coalition agreement conservative and SPD leaders struck last month “is no furious firework of innovation”.

“The coalition agreement is a large compromise document,” Spahn, who is due to become health minister if the coalition takes office, told Handelsblatt business daily.

Spahn’s lukewarm support for the coalition deal highlights the risk that the alliance proves fractious and unstable.

The inclusion in the deal of a clause that envisages a review of the next government’s progress after two years has fueled a debate about a succession plan for a post-Merkel era.

On Monday, Merkel ally Annegret Kramp-Karrenbauer won election as CDU general secretary, putting her in pole position to succeed the chancellor after spending most of her career in a tiny state on the French border.

Spahn said he would support Merkel for the full legislative period and she should remain CDU leader through to 2021.