The political fate of Japan’s youngest postwar Prime Minister may be decided by the one person in the country who can still tell him what to do — his mother. Shinzo Abe’s staunchest rural support base has deserted him and the ruling Liberal Democratic Party’s own MPs are campaigning openly against their leader.

But it will be Yoko Abe, the 79-year-old matriarch of perhaps Japan’s greatest political dynasty — the daughter, niece and mother of three prime ministers — who judges tomorrow whether her son must fall on his sword.

A fiasco that has left millions unsure about their pensions, three Cabinet resignations and worsening disparities between rich and poor have combined to threaten the 52-year monopoly of the LDP. Mr Abe, as its leader, is reaping what one senior party member called “decades of pent-up hatred”.

The ruling party’s punishment in tomorrow’s upper house elections is virtually assured: rarely have Japanese opinion polls agreed so closely on the ferocity of voters’ discontent. But it is the margin of defeat that will sway Mrs Abe. Close sources toldThe Times that if the LDP collapse is deemed sharp enough to heap dishonour on the noble house of Kishi, she will demand that her son resign.

It is thought that Mr Abe’s precipitous drop in popularity may have embarrassed Yoko already. As campaigning has grown dirtier and more desperate, his tone has cracked from confident to pleading. Mr Abe, campaigning in the rural province of Echizen this week, concluded his speech: “Please, please give us power. We’ll keep our promises.”

Some lower house MPs are preparing quietly for a snap general election. Half of the 242 upper house seats are up for grabs tomorrow. To maintain its majority the LDP must win 50 seats and New Komeito, its coalition partner, must hold on to its current 14.

With what LDP campaigners are describing as a “typhoon headwind” against it, the ruling party is expected to hold only between 40 and 43 seats. Some analysts believe that Mr Abe’s party may win fewer than 40, and more than half the country thinks that the Prime Minister should resign if the LDP matches its 1989 low of 36 seats secured in an upper house election.

Technically, Mr Abe’s job is not threatened. The LDP won a landslide victory in the 2006 lower house elections and retains a comfortable coalition majority there. But an upper house under the control of the opposition Democratic Party of Japan would have the power to derail many of Mr Abe’s vaunted reforms. A DPJ speaker would be Japan’s first non-LDP leader of the upper house since the Second World War.

According to analyst Takao Toshikawa, the LDP’s decades of incumbency, once its biggest asset, have now become a liability. Until two years ago more than 100 sitting LDP politicians “inherited” their political bases from their fathers. Mr Abe, the blue-blood scion who did not win a general election to become Prime Minister, is viewed as the ultimate expression of this.

When he assumed power last autumn, Mr Abe inherited an electorate that was promised change under his predecessor, Junichiro Koizumi, but no longer believes the LDP machine is capable of delivering. The trend is most pronounced in the single-seat rural constituencies — the 29 seats where the LDP is expected to receive its fiercest backlash.

Mr Toshikawa believes that Mr Koizumi’s shadow looms over this election. In the cities, where the former Prime Minister’s reforms were embraced, Mr Abe’s poor reformist credentials draw criticism. In the countryside, which bore the brunt of Mr Koizumi’s efforts to smash the old LDP support base, the squeeze of reform is unbearable. While Mr Koizumi had the charisma to deliver his “pain before gain” agenda, Mr Abe has not.

Iwao Kato, an elderly voter in one of those constituencies, on the island of Shikoku, said: “The LDP has simply held on to power for 60 years and we must show that Japan is not like China politically. The imbalance between the regions and the cities has been allowed to go too far.”

Despite the expected drubbing for the LDP, many are unhappy with the options presented. The DPJ, whose campaign has been masterminded by Ichiro Ozawa has become the default protest vote and has yet to persuade many voters it is ready to run the entire country. Mr Ozawa has been forced to abandon many core policies in order to attract conservative voters who are simply tired of the LDP.

Unlikely contenders

The strength of antiLDP sentiment has given hope to candidates who would normally not stand a chance. Many believe that surprise victories may be in store for:

- Alberto Fujimori Former President of Peru running while under house arrest in Chile. It is unclear whether he will be allowed to come to Japan

- Yuko Tojo Granddaughter of Japan’s most notorious Class-A war criminal. Her election posters show a flock of white doves, but her main passion is for the Yasukuni war shrine and for Japan to rediscover its nationalism

- Mac Akasaka Entrepreneur who runs a “Smile Clinic” where patients are trained to flex face muscles. Has been campaigning by driving around Tokyo with Eighties dance tunes blaring from a small van

- Yoshihiro Nakamats Elderly “boffin” who invented the floppy disk and claims to be able to design a force field protecting Japan from North Korean missiles

Times Recommends

• It’s only Brits who don’t appreciate me, says Blair
• Party’s over for Greek graspers
• White House tightens security for Xmas marathon