While Westminster’s rain-sodden parliament roof risks falling in, the glass dome on Germany’s federal parliament in Berlin may soon blow off – due to overcrowding.

By law the Bundestag has 598 MPs but since it moved to the historic Reichstag building in Berlin 20 years ago, the number of seats has been on the wrong side of 600.

The 2017 federal election cracked a new record, with electoral law curiosities resulting in 709 seats, costing taxpayers €973 million annually.

And, if Germans went to the ballot box now, a new projection suggests the next parliament would have to find room for 804 MPs at a cost of €1.04 billion a year. Bundestag president Wolfgang Schäuble has sounded the alarm, telling his Christian Democratic Union (CDU) on Tuesday that the ballooning Bundestag is undermining voter confidence in parliament.

“There’s no way the Bundestag can explain that it cannot change electoral law because it cannot find a solution,” he said. A year ago, the 76-year-old promised reform and that, as the Bundestag’s new president, he “wouldn’t allow failure”.

But he underestimated just how attached many MPs were to their €10,074-a-month jobs.

PR elections

Germany’s Bundestag is elected by proportional representation, with two votes on each ballot paper.

The first vote is for a direct candidate for each constituency, of which there are 299, and a second vote for a party list. This second vote determines which proportion of the 598 regular seats a party has won. Should a party win more (first vote) direct constituency seats in a federal state than its second vote share allows, the direct candidates remain on as “overhang mandates”.

The system was devised to boost fairness but, since unification in 1990, has had the opposite effect. In 2012 the federal constitutional court demanded the system be reformed with no more than 15 overhang mandates allowed in future. Seven years and two federal elections later, the current Bundestag has a record 46 overhang seats.

Wolfgang Schauble: his CDU party holds 78 per cent of overhang mandates in the current Bundestag. Photograph: Emmanuel Dunand/AFP/Getty

Dr Schäuble’s new proposal would reduce to 270 the number of constituencies, and thus the number of overhang mandates.

This was backed by the Social Democratic Party (SPD), Greens, liberal Free Democrats (FDP) and Left party. But Dr Schäuble’s own Christian Democratic Union (CDU) revolted.

Most of its MPs are elected through the direct, first vote, while the CDU holds 78 per cent of overhang mandates in the current Bundestag.

Jobs for the boys

Dr Schäuble’s party insisted its concern was not about jobs for the boys but the quality of democratic representation. Reducing the number of constituencies and increasing their size would, the CDU argues, increase even further the 1:87,000 MP-to-voter ratio.

The CDU proposal: increase the number of seats to 630 and abolish the overhang mandates, a proposal rivals say would disproportionately benefit Chancellor Angela Merkel’s ruling party.

With no compromise in sight, the cracks keep building in the German parliament’s glass dome, beneath which German MPs cost taxpayers – in salaries and allowances – €739,000 annually. While the House of Commons is struggling with ordinary rain, in Berlin’s Bundestag it’s raining money.