When Wolfgang Schauble, leader of Germany's opposition Christian Democrats, rolled his wheelchair through the door of Helmut Kohl's office on Berlin's Unter den Linden last Tuesday morning, he knew he was on a mission without hope. A lifelong political friendship between Schauble and his predecessor as party leader had already deteriorated into a bitter power struggle that only one of them could survive.

Schauble asked Kohl to identify publicly the donors of up to £1 million the former chancellor has admitted accepting in cash during his last five years as chancellor. Some 40 minutes later, after an encounter aides described as "very noisy", a grim-faced Schauble left for a meeting of his party's 43-strong leadership executive.

By the end of that day, Schauble had won the full backing of the meeting and Kohl had resigned as honorary chairman of the CDU, bringing to a humiliating end one of the most distinguished political careers in German history. By the end of this week, the CDU official in charge of the parliamentary party's finances had hanged himself and the party leadership was preparing to take legal action against Kohl.

The scandal surrounding illegal payments to the CDU has been so dramatic and fast-moving, with new revelations of wrongdoing almost every day, that the German public is hard pressed to keep pace. But one factor has remained constant ever since the scandal broke last November - Kohl's stubborn silence about the source of his illegal funds.

The former chancellor claims that he promised donors that they would remain anonymous and that he is not prepared to break his word to them.

"I have never in my life abandoned my honour and I will not do it now either. That involves keeping a word of honour I have given," he told an appreciative audience of Hamburg businessmen this week.

Even if Kohl is telling the truth - and it is difficult to find anyone in Berlin's political scene who believes him - he has yet to explain why he values his own private promise more highly than the oath he took five times to remain true to the constitution.

The former chancellor's lawyers are understood to have advised him that, despite the current criminal investigation against him, he is in little danger of being prosecuted on the basis of what is already known. But they have warned him that any public statement he makes could endanger his position and raise more perilous questions.

The number of unanswered questions about the CDU's financial affairs is already dizzying and Schauble warned the party this week that new revelations were imminent.

Kohl has admitted accepting £1 million in anonymous donations between 1993 and 1998 and channelling the money through secret accounts to local party activists. Some of the funds went to Kohl's own constituency in the Rhineland Palatinate and activists in the northern state of Schleswig-Holstein have admitted receiving a secret transfer.

Some commentators have suggested that one reason Kohl will not name the donors is because they did not, in fact, exist. They suggest that the £1 million may have come from secret accounts in Switzerland and Liechtenstein used by the CDU to disguise the origin of illegal donations.

The party in Hesse admitted last week that it made regular transfers from a Swiss account, disguising the money as bequests from CDU supporters. In a tasteless twist, the party claimed that these non-existent supporters were Jewish survivors of the Holocaust. Police yesterday searched the home of Wolfgang Hullen, the head of the finance office of the CDU parliamentary party, who hanged himself on Thursday morning. Contrary to an initial statement by the party, Hullen's suicide note is understood to refer to financial irregularities and to confess that he stole money from party funds.

Most worrying for Kohl is an investigation by Geneva prosecutors into an alleged DM85 million in bribes paid by the French oil company Elf Aquitaine in connection with its purchase of an eastern German oil refinery in the early 1990s. Prosecutors have frozen accounts held in Liechtenstein by Dieter Holzer, a lobbyist with close links to Kohl and they are investigating some of the former chancellor's most trusted associates.

The former chancellor denies being bribed by Elf Aquitaine and insists that donations to party funds never influenced government policy, but files relating to the oil refinery sale disappeared mysteriously from the chancellery before Kohl left office.

The CDU is bracing itself for fresh revelations when an auditor's report on the party's finances is published but many activists fear that the real danger to the party's future lies in its breach with its former patriarch. Kohl is convinced that his successor has mishandled the funding scandal by making too many confessions too soon and, although he will never himself occupy a party position again, he appears determined to destroy Schauble's leadership.

Vengeful and unrepentant, Kohl will do anything in his power to preserve his place in history, even if it involves wrecking the party he led for a quarter of a century.

AFP adds: Mr Helmut Kohl told a CDU meeting in Bremen yesterday that he would not name donors to secret party funds since he had promised them anonymity. "It's an outdated principle, but I am outdated. I must keep my word," said Mr Kohl, repeating a position for which he has been sharply criticised by party leaders.

Mr Kohl was presenting new year's greetings to a partisan crowd in Bremen, northern Germany, who frequently interrupted his speech with applause. Appearing drained by the scandal, Mr Kohl added in a bittersweet note: "In a few weeks, I will be 70. I do not want honours but simply to live. I was, I am still, a member of parliament for 40 years."