Sweden’s election authority says it is getting ready for snap elections as far right prepares to vote with opposition, potentially forcing centre-left government to fall

Sweden is on the brink of political chaos after the far right said it would exploit its kingmaker role in parliament to stop the centre-left coalition from passing a budget, potentially forcing the government to fall.

The worst fears of Social Democrats and Greens were realised on Tuesday night when the anti-immigration Sweden Democrats announced they would vote with the centre-right bloc to kill off the government’s financial plans on Wednesday.

Even with the votes of the Left party of former communists, the red-green coalition does not command a majority in parliament, making it vulnerable to the far right’s break with tradition to vote with the opposition.

“There is an option to try again, there is an option to resign, and there is an option to call new elections,” the prime minister, Stefan Löfven, told Swedish news agency TT after talks with the centre-right broke down.

Swedish politics faced a new situation in which the Sweden Democrats believe they can prevent all policies that do not lead to lower immigration, he said, calling the party’s behaviour “exceptionally irresponsible”.

The Alliance bloc of four centre-right parties has turned down frequent overtures from Löfven to break rank and strike deals with the government. Many believe they should seize this moment to destroy the red-green government and force Löfven to rule without the Greens or call new elections. A government of Social Democrats alone would be even weaker than the current coalition and would be forced to horse-trade with the centre-right.

But the Alliance risks being seen by voters to be relying on the far right to bring down the government. The Sweden Democrats are treated as pariahs by the mainstream parties and the media, but they more than doubled their vote in September elections to almost 13% on the back of rising hostility to immigration.

Parliament could return the budget to the finance committee for further deliberation and to buy time, but such a move only makes sense if there is a possibility that Alliance will agree to collaborate. Alliance party leaders have made clear they have no intention of doing so.

“It is not the opposition’s responsibility to get the government’s budget through parliament … There are significant differences between our budgets,” Anna Kinberg Batra, interim leader of the Moderate party, the largest in the Alliance, said on Tuesday night.

Liberal daily Dagens Nyheter said the prospect for lasting and stable majorities in parliament appeared minimal. “The mainstream parties do not seem to understand each other, and hardly even themselves,” it said.

“The Sweden Democrats will act to try to stop any government that chooses to pursue a growth in immigration and gives the Green party a decisive influence on Swedish migration policy,” said Mattias Karlsson, Sweden Democrats’ leader in parliament, at a press conference on Wednesday.

“It is reasonable to speak to us and hear what our more than 800,000 voters think.”

Newspapers and television channels interrupted live transmission of the Sweden Democrats’ press conference in a mark of mainstream outrage that the far right should exploit the situation to push its demand to slash immigration by 90% from its current high levels as refugees flee conflict in Syria, Somalia and Iraq. One tabloid called it “a PR coup” by the Sweden Democrats.

Parliament begins voting on the different parties’ budget proposals at 3pm GMT.

Sweden’s election authority said it was preparing for snap elections and had put in an order for 6m ballot envelopes.

Sweden has a long history of minority governments because the opposition has traditionally opted not to unite behind a common alternative budget, enabling the Social Democrats for long periods to reign in the minority.

“A government without a budget is no government, and Stefan Löfven has already made it clear that he would rather resign than rule with the Alliance’s budget,” wrote commentator Göran Eriksson in Svenska Dagbladet, a rightwing daily.

As the sense of crisis surrounding the government grew over the past weeks, the paper repeatedly called on the government to quit.