The clash of the political bluebloods -- incumbent Taro Aso and his rival Yukio Hatoyama -- casts a spotlight on Japan's rich and powerful clans that have dominated, and some say stifled, post-war politics.

About one third of Japan's parliamentarians are hereditary politicians -- often derided as "botchan" or "babies from rich families" -- who inherited their districts and fund-raising bodies from a relative, usually their father.

Japan's politics often a family business AFP – Democratic Party of Japan leader Yukio Hatoyama displays a leaflet of the party's manifest for the …

In many areas, politics as a family business has all but shut out the possibility of fresh blood -- just ask Katsuhito Yokokume, a 27-year-old candidate for Hatoyama's opposition Democratic Party of Japan (DPJ).

Yokokume, a lawyer and the son of a truck driver, has campaigned hard in Yokosuka, a port city south of Tokyo, hoping to wrest the seat from Aso's conservative Liberal Democratic Party (LDP) in the August 30 election.

But, even with the DPJ leading in the national polls, Yokokume -- who criss-crosses the constituency on his bicycle and chats with railway commuters day after day -- admits he is fighting an uphill battle.

His opponent is Shinjiro Koizumi, the son of charismatic former premier Junichiro Koizumi, who ruled Japan until 2006.

"Before discussing anything substantial about political pledges, I have to ask voters to remember my face and name in this Koizumi dynasty (area)," said Yokukume, who graduated from a top university in Tokyo on a scholarship.

"I raised my hand to run in this constituency because what Mr. Koizumi has done is exactly the opposite of what I want to realise as a politician... I want to change politics to represent the views of ordinary people."

When the elder Koizumi last year announced he would not contest his Diet seat again, he apologised to supporters for his "blind parental love" -- and then urged them to support his 28-year-old son and anointed successor.

If elected, the younger Koizumi will be the district's fourth-generation representative -- carrying on what a local assemblyman derided as "a dynasty with a longer history than that of North Korea's Kim Jong-Il."

Yokokume's hopes were lifted when an independent mayoral candidate in June beat the incumbent supported by Junichiro Koizumi -- but he is under no illusion that taking on one of Japan's political aristocracies will be easy.

Criticism of the system has intensified especially since two recent LDP prime ministers -- Shinzo Abe and Yasuo Fukuda, respectively the grandson and son of former premiers -- unexpectedly quit after just one year in office each.

"Since these resignation dramas of the past few years, the public image emerged that second- and third-generation politicians are spineless," said Tomoaki Iwai, professor of politics at Nihon University.

"But the real problem with hereditary candidates is that they inherit their family members' political support groups, thus blocking newcomers from entering politics," the professor said.

Many of Aso's current and former cabinet members come from political families, including former finance minister Shoichi Nakagawa, who quit in February after appearing drunk at a media conference.

Few politicians epitomise the trend like Aso and Hatoyama, whose paternal grandfather Ichiro Hatoyama became the LDP's first premier in 1955, taking over from Aso's grandfather Shigeru Yoshida, who led a forerunner of the LDP.

Hatoyama insists he is not a hereditary candidate because he has run in a constituency different from his father's.

Responding to popular dissatisfaction with hereditary politics, the DPJ has pledged that, if it wins government, it would bar children, grandchildren, nieces and nephews of its members from running in the same constituencies.

The LDP has toyed with a similar policy this year, but the ruling party has so far made no official campaign pledge on the issue.