At a record size of 709 lawmakers, the German Bundestag is the largest democratic chamber in the world. The only Parliament that is any larger is the Chinese National People's Congress.

With the clock ticking until the next federal elections in fall 2021, a top-level coalition committee met on Tuesday in a bid to prevent the Bundestag ballooning even further.

The solution, however, must be agreed upon by all three parties in the Grand Coalition government — Chancellor Angela Merkel's Christian Democrats (CDU), their Bavarian sister party the CSU, and the Social Democrats (SPD). None of which are prepared to risk foregoing power and influence. But without change, critics fear that more than 800 lawmakers could be crammed into the Bundestag after next year's elections.

Proportional representation

Germany's system of mixed-member proportional (MMP) representation has been used since the Federal Republic was founded in 1949 and was later carried over into reunified Germany. Back in 1949, fears — and fresh memories — of a fragmented party system and political instability meant that a system built purely on proportional representation was off the cards.

Read more: Is it hard for blind people to vote in Germany?

But smaller parties also opposed a straight up first-past-the-post system, as it would make winning seats extremely difficult for them. In the end, the MMP system was deemed the right fit for post-war Germany and for decades was regarded as a model by western observers: it respects political minorities while also preventing party fragmentation. But 70 years has taken its toll on the Bundestag's waistline and Germany's Parliament is running out of buttons to undo.

In theory, the Bundestag has 598 seats, half of which are filled by directly elected lawmakers. The rest are for MPs selected from candidate lists. So where are the other MPs coming from?

"Overhang" mandates

When Germans head to the polls, usually every four years, each voter casts two votes on their ballot paper: one for the constituency representative and one for the party. Whoever receives the most votes is guaranteed a seat in the Bundestag: a direct mandate.

The second vote determines the relative strength of the parties — of which there are currently seven sitting in Parliament. The parties therefore receive as many mandates in the Bundestag as they're entitled to according to their share of secondary votes.

If a party wins more seats than it's entitled to, based on the share of second vote results, they are allowed to keep them. These are the "overhang" seats. Conversely, if a party receives fewer direct mandates than it is entitled to, then it is awarded the extra seats from its party's candidate list. The aim is to maintain proportionality in the Bundestag.

In the last federal election in September 2017, that resulted in a total of 111 extra seats. 

Hey, big spender!

A bigger parliament comes, naturally, with bigger costs. The Bundestag budget could tip the €1 billion mark this year, marking an increase of 25% on the first full financial years of the 2014 and 2018 legislative periods, reports a research paper by Deutsche Bank.

But the effects are more than financial. "The problems start with the most banal,” said Sophie Schönberger, professor of Public Law at the University of Düsseldorf. "More MPs means more physical seats in the Bundestag and more office space.”

With the parliamentary building complex already bursting at the seams, plans are underway to set up a container village for the potential overflow of new MPs.

More lawmakers also means an impractical Bundestag, with more speeches, committees and initiatives. "The bigger parliament is, the less effective its work will be," Schönberger added.

Electoral reform: a German political hobby

The latest proposals to reform Germany's electoral system are by no means the first. But none have ever made it out of the starting blocks. It was just a matter of weeks ago that the two conservative parties, the CDU/CSU, finally managed to agree on a proposal. That would see the number of constituencies reduced from 299 to 280 and non-compensation of up to seven overhang mandates.

But other parties claim this would violate the basic structure of proportional representation — not to mention the constitution. As the strongest party, the proposal would be advantageous for the conservatives.

The SPD meanwhile has proposed an interim, "transitional solution" to limit the number of seats in the Bundestag to no more than 690. No more overhang seats would be designated. But that could mean that parties who win more direct mandates than they are entitled to proportional to secondary votes, would have to give some of them up.

Currently, that would only affect the CDU/CSU.

The conservatives say the non-allocation of overhang mandates is unconstitutional. The proposal could also risk a situation where not all constituencies have an elected representative.

A third option put forward by the three opposition parties was not on the table at Tuesday's talks. The business-friendly Free Democrats, the Left Party and the Greens all want to radically reduce the number of constituencies from 299 to just 250.

But such a radical move is easier said than done. The redrawing of constituencies is not only geographical. Demographics also have to be taken into account, which would require time the Bundestag simply doesn't have before voters head to the polls. According to an informal rule, electoral law cannot be changed within a year of a federal election.

Positive news of an agreed electoral law reform on Tuesday would be nothing short of a political miracle. But, it would by no means be the first time that Merkel has conjured up a last-minute compromise.

Volker Witting also contributed to the article.