'It's a clever ploy,' said Noriko Hama, a professor at Kyoto's Doshisha University. 'Mr Koizumi has made this election into a single-issue vote and not a lot of people will want to be seen to be opposed to reform of Japan's structural problems.

'If it was merely a question of the public wanting a change of government then it would be simple - vote for the opposition Democratic Party of Japan (DPJ) - but it's not,' she said. 'I'm not a big fan of Mr Koizumi or his policies and I've never voted for him, but I think even I will have to vote for him this time around.'

Mr Koizumi opted to go to the voters on Monday after rebel members of his Liberal Democratic Party sided with the opposition parties in the upper house of the Diet to defeat his legislation to privatise Japan's postal service.

Election day has been set for September 11, with Mr Koizumi vowing to resign as LDP leader if the electorate refuses to give him the mandate to continue with his reforms. Victory will severely weaken the rebels within his party and enable him to push the postal privatisation into law.

DPJ politicians greeted the election announcement with glee. Party president Katsuya Okada said: 'A DPJ administration would proceed with real reforms and I see this dissolution as an opportunity to revamp Japan.'

Go Ito, a political science professor at Tokyo's Meiji University, said the DPJ 'are sure to think they have a good chance, but the party has a lot of problems. There is a great deal of disagreement within the party and they don't have definite policies. An opposition needs to have thought before it fights an election.'

The party could gain sufficient support through deals with minor parties, Professor Ito concedes, but a weak, divided government could lead to a political crisis and a return to the instability of a different prime minister every 12 months that plagued Japan in the 1990s.

'Japan really needs these reforms now because the rapid growth of the 1960s and 1970s has gone,' he said. 'We are at a crossroads in politics and even though Mr Koizumi has been able to break the pork-barrel politics of the past, we would go straight back to that if the old-guard LDP managed to gain the upper hand again.'

There are even those who suggest Mr Koizumi was not too disappointed at Monday's defeat in the House of Representatives since it will allow him to complete another promise made when he was elected LDP leader: to destroy a party still living in an era of patronage and the politics of a wink and a nod.

'If Mr Koizumi wins in September, there will be nothing standing in his way. He will have a mandate for even more radical reforms,' says Professor Hama. 'He really can have his cake and eat it.'