I’ll use the British Parliament structure but as a hypothetical example.
Let’s say that after the election, the Right Party gets 235 seats, the Middle Party gets 215 seats, and the Left Party gets 200 seats. So no party has the 326 seats needed to be a majority (Parliament having 650 seats in total), a coalition government needs to be formed, and a coalition of any two parties would be enough to form a majority.
Now Prime Minister Smith, the head of the Middle Party, is the incumbent PM so he gets first shot at forming a new government. Suppose he goes to the Right Party and says, “We prefer you guys to the Left Party and we know that you prefer us to the Left Party, so we’d rather form a coalition with you. But here’s the deal. I want to stay in power as Prime Minister. You can be a partner in the government but we’re going to be the more leading partner even though you have more seats. And if you don’t agree to this, we’ll just go to the Left Party instead. They prefer us to you and they’ll be willing to be the junior partner to us because they have less seats. And we’d rather be the leading partner in a coalition with them than the junior partner in a coalition with you.”
From the Right Party’s point of view, this is the best deal they’re going to get. They know that everything Smith said is true. They’d like to be the leading partner in a coalition but it’s not going to happen. They’ll either be the junior partner in a Middle/Right government or they’ll be the opposition to a Middle/Left government. With those two choices, accepting Smith’s offer is the best altenative.
But, here’s my question. Is such a deal possible? Can a party with more seats voluntarily agree to being the junior partner in a coalition government? Or is the largest party in the coalition automatically the leading partner (with the head of that party becoming the Prime Minister)?