Japan was in political turmoil last night after the sudden and puzzling resignation of the Prime Minister, Yasuo Fukuda, after a year of parliamentary deadlock and failed attempts to invigorate the economy.

There was no obvious trigger for the announcement, the second change of leader in less than a year, which opens the way for the right-wing nationalist Taro Aso to become prime minister and increases the likelihood of a general election in the next few months.

Mr Fukuda’s announcement took the Japanese political world by surprise, and his explanation – that he wished to hand over power to a new leader in advance of a new session of parliament – was puzzling, given that the next prime minister is certain to face difficulties just as punishing as he did.

“I thought there should be a force to take things forward,” he said in nationally televised press conference. “There should not be any political vacuum. A new force will be needed to implement policies, so I have decided to resign.”

The resignation does not mean a change of government immediately. Instead, the ruling Liberal Democratic Party (LDP) will choose a new leader who, thanks to the party’s majority in the Lower House of the Diet, is guaranteed election as prime minister.

The problem lies in the Upper House, where the opposition Democratic Party of Japan (DPJ) has been using its majority to block and delay legislation and decision-making in an attempt to force a general election.

Mr Fukuda’s decision was denounced immediately by the secretary-general of the DPJ, Yukio Hatoyama. “I am deeply resentful towards Fukuda for not caring about people,” he said. “His sudden abandonment showed that the LDP does not have the ability to hold the reins of government. All we want is the calling of early elections.”

Sapped by the parliamentary deadlock, Mr Fukuda, 72, has suffered dismal approval ratings for most of his 11½ months in office, but there were no obvious signs that September was going to be much more awful than every other month. He reshuffled his Cabinet and only last week presented a 12 trillion yen (£60 billion) economic stimulus plan. Its measures, such as lower tolls on the roads and bailouts for small businesses facing bankruptcy, were dismissed by market analysts as a clumsy collection of vote-grabbing initiatives.

Neither the reshuffle nor the cash injection showed any sign of lifting the popularity of his Government, and fresh political problems made it certain that a special Diet session scheduled for next week would be as gruelling as the last.

From the beginning, Mr Fukuda gave the appearance of being a mildly reluctant Prime Minister who never cared all that much whether he kept the job.

His father, Takeo Fukuda, was Prime Minister in the 1970s and his aunt, brother-in-law and nephew have all been MPs, but for the first 17 years of his career he served as a conventional Japanese salaryman in an oil company.

He took over after the resignation, a year ago next week, of Shinzo Abe, having agreed reluctantly to stand against Taro Aso, who will now almost certainly take over his job. Mr Aso, the 67-year-old secretary-general of the LDP and former Foreign Minister, is a conservative who favours a close alliance with the US and has offended minority groups, as well as Japan’s Asian neighbours, with his outspoken opinions.

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