Speaking at the start of a three-hour parliamentary debate, Andersson acknowledged that joining Nato represented a “historic change in our country’s security policy approach”, and that neutrality and non-alignment had been beneficial for Sweden. 

“This is not a decision that you make easily, but despite fact that non-alignment in its various forms has served Sweden well for 200 years, it is my judgement that it is not going to serve Sweden as well in the future,” she said. 

“There are so many things in Sweden that are worth defending, and Sweden can be best defended within Nato.”

After the debate, Andersson is due to meet with her ministers to take the formal decision to join the alliance, with the application to be delivered to Nato’s headquarters in Brussels by Sweden’s Ambassador to the alliance, either today or early this week. 

In her speech, Andersson underlined that Article 5, the mutual defence clause at the core of the Nato alliance did not only mean that other countries would come to Sweden’s aid if it were attacked, but also meant that Sweden would not be able to remain passive if allies were invaded. 

What would not change, she promised, was Sweden’s ability to pursue an independent foreign policy focused on equality, democracy, human rights, and nuclear disarmament. 

Sweden, like Norway and Denmark, would soon declare that as a Nato member, it does not want to host nuclear weapons or permanent Nato bases on its territory. 

Swedish speakers can read Magdalena Andersson’s speech here. 

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The Moderate Party’s leader, Ulf Kristersson, toned down his past criticism of the Social Democrats’ longstanding opposition to Nato membership, instead praising Andersson for the way she has managed the process. 

“I would like to convey my appreciation to Magdalena Andersson,” he said. “We have had regular contact and discussed the consequences for Sweden of the new security policy situation and I have placed great value on those discussions.” 

Concerning Russia, he said he wanted to repeat the words of Sauli Niinistö, Finland’s President: “Putin, look at yourself in the mirror. It is you who has caused this.” 

Nooshi Dadgostar, leader of the Left Party, the party that most staunchly opposes Nato membership, complained that Sweden’s decision-making process had been rushed and undemocratic. 

“It’s deeply serious that voters have neither been able to give their opinion on this in a referendum or in an election,” she said. “This undermines the legitimacy of the decision. This process is a betrayal of the voters. The decision has been taken over the top of voters’ heads.” 

Sweden’s debate started one hour after a similar parliamentary debate in Finland, after which, unlike in the Swedish parliament, a vote will be taken on Nato membership. 

“Our security environment has fundamentally changed,” Finland’s prime minister, Sanna Marin, told parliament at the start of the session. “The only country that threatens European security, and is now openly waging a war of aggression, is Russia.”

An overwhelming majority of Finland’s 200 MPs — at least 85 percent — back the decision to join Nato after Marin’s Social Democratic Party on Saturday said it was in favour of joining.

Speaker of parliament Matti Vanhanen said “over 150 requests to speak were made” and the vote was not expected to take place on Monday.

Public opinion is also strongly in favour of membership. According to recent polls, the number of Finns who want to join the alliance has risen to more than three-quarters, almost triple the level seen before the war in Ukraine began on February 24.

Finland, which shares a 1,300-kilometre (800-mile) border with Russia, was invaded by the Soviet Union in 1939.

Finns put up a fierce fight during the bloody Winter War, but were ultimately forced to cede a huge stretch of their eastern Karelia province in a peace treaty with Moscow.