The choice of fruit belies a poisonous and often violent campaign that has sharpened ethnic divisions in multi-tribal Kenya to a hitherto unknown degree. Some fear the campaign could lead to the break-up of the ruling National Rainbow coalition.

The referendum is also seen by many as a spectacular betrayal by the government of President Mwai Kibaki. When he came to power in December 2002 on a tide of popular and cross-party support, promising reform and the end of corrupt rule, he inherited almost dictatorial powers from his predecessor, Daniel arap Moi.

At the time, Kibaki supported a new constitution that would cede some power to a prime minister he more or less promised would be Raila Odinga, a leading opposition figure who did more than anyone to help him win the presidency.

Once in office, however, Kibaki and his ministers — mostly from his Kikuyu ethnic group and nicknamed the Mount Kenya mafia — went back on their word. Kibaki has shown that he does not like losing power any more than Moi, whose 24-year autocratic rule was notorious for abuse, corruption and repression.

A draft constitution that would have diluted the president’s power has been mangled by his government so its members can preserve their newly won powers of patronage.

They are determined to prevent Odinga, who is minister of roads and public works and is not a Kikuyu, from gaining power and have thrown out the idea of an elected prime minister.

If the bananas win, which seems virtually certain given the accusations of harassment, intimidation and bribery, Kibaki’s presidential powers will be reinforced, not reduced.

“I will eat my hat if the bananas lose,” said a western diplomat. “The issue is how convincing their majority is. They can win with 51% but morally they need to get 65% or 70%.”

The government has also tried to make the referendum a distraction from the overriding issue plaguing Kenya today — its record on tackling corruption. But the referendum is far from irrelevant to corruption.

One of the proposals in the original draft dropped by the government was the abolition of the president’s office.

The problem was identified in a speech in July last year by Britain’s high commissioner, Sir Edward Clay. He said corruption had cost Kenya $188m (£109.2m) since the Kibaki government came to power. He accused ministers of “eating like gluttons” and “vomiting on the shoes” of aid donors, and presented Kibaki with a dossier of corruption cases.

Clay retired in the summer. But Britain seems determined to keep up the pressure. Its continuing stand over corruption has made relations with its former colony frosty. London is locked in a dispute with Nairobi over renewal of a 40-year-old agreement for the British Army to train in Kenya and is threatening to abandon war games unless it is finalised.

A victory for the bananas tomorrow will almost certainly also feed the ambitions of Kibaki, 73, to stand for a second term in 2007 despite his undertaking before his election that he was a “one-term president”.

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