For one thing, single-party states are almost invariably dictatorships. That would be an obvious reason why many would oppose it.
Obviously several people in the single party would have radically different political views. You should make up a big domestic issue that would be very polarizing. This would cause MPs to immediately form named factions that would become political parties.
Another idea could be a hotly contested election. For example, in 1824 the United States had become a
de facto single-party state, with the Democratic-Republican Party having a super-majority in Congress, and the only opposition party, the Federalist Party holding a negligible amount of seats. In the
1824 presidential election, four different candidates from the Democratic-Republicans ran for president, the bitter factionalism between the top two candidates (John Quincey Adams and Andrew Jackson) and their supporters eventually resulted in a schism; the party split into the Democratic Party and the National Republican party (which later formed into the Whig Party, and later on the modern Republican Party).
Perhaps you should explain more about Syrixia's political system. Who is Alfred Nursson? What are his policies like? How is he elected?
It's important to note that Syrixia does
not technically have a parliamentary system of government. A parliamentary system is
by definition a system wherein the executive government is approved by, and accountable to the legislature. In most parliamentary governments, the members of the executive branch are themselves members of Parliament. Some have what's called a Norwegian law, (as Norway is where this convention originates) where members of the executive are chosen from among members of parliament, but must resign their legislative positions once they are chosen. Parliamentary governments also have a separate ceremonial head of state. In some cases it is a monarch, in others it is an elected president. There are exceptions to this rule, South Africa has a President who is the equivalent of a Prime Minister. The actual PM is pretty much a glorified secretary.
I hope this information is helpful to you, and I am interested in this RP.