There was no mistaking the anger of the former chancellor, Helmut Kohl, as he made a rare intervention in the Bundestag this week to deny allegations that he knew of a DM1 million (£403,000) gift to his Christian Democrats from an arms dealer who is now wanted by the police. The government has set up a parliamentary commission to investigate claims that the money was linked to Dr Kohl's approval of a lucrative arms deal with Saudi Arabia.

"The slander that is taking place here cannot be permitted. I call on you to open this parliamentary inquiry without delay and to give me the chance, before Christmas, to answer the questions raised," the former chancellor said.

Most observers believe Dr Kohl when he says he was unaware of the DM1 million handed in cash to his party's former treasurer, Walther Leisler Kiep, in 1991. And there is no suggestion that Dr Kohl ever benefited personally from any donation to his party.

But many party colleagues expressed bewilderment about the former chancellor's ignorance of the Christian Democrats' finances, because he took such a keen interest in every detail of the organisation he led for more than a quarter of a century. Some Christian Democrats condemned his emotional outburst in the Bundestag as unwise, warning darkly that more revelations could be on the way.

Those revelations came yesterday when Heiner Geissler, a former general secretary of the party, confirmed that the Christian Democrats channelled donations through a number of secret accounts. By keeping such cash out of its official budget, the party was able to keep donors' names secret.

"Apart from the budget of the federal party, there were other accounts, that is true. I always believed that was wrong and it must be cleared up now," Mr Geissler said.

According to a report in yesterday's Suddeutsche Zeitung, the party had at least 10 secret accounts, through which funds were channelled to local organisations. These accounts were set up by Horst Weyrauch, a long-serving party accountant and close confidant of Dr Kohl's.

The DM1 million to Mr Kiep was paid into one of the secret accounts, and prosecutors investigating the payment found documents detailing transfers to local party groups. Many of these documents bore the letters PV, an abbreviation used among Christian Democrats for Parteivorsitzender or party chairman, the position held by Dr Kohl.

One document, for example, bears the reference "PV300000SH", which prosecutors interpret as "party chairman approves DM300,000 for Schleswig-Holstein".

Political observers have long been puzzled by the speed with which the Christian Democrats turned a DM43 million deficit in 1989 into a surplus of DM23 million in 1991. According to German law, political parties are not obliged to disclose the origin of donations worth less than DM20,000; a rule the Christian Democrats appear to have circum navigated by encouraging donors to split large donations into smaller sums.

There are tough financial penalties for parties that fail to declare large donations, and the Christian Democrats' DM1 million gift from the arms dealer could cost them up to DM13 million in fines. But the party could face an even worse fate if, as investigators suspect, it avoided paying tax on donations by opening bank accounts in Switzerland.

Dr Kohl's claim that he knew little of his party's finances is contradicted by Eberhard von Brauchitsch, a former representative of the Flick steel company, which was at the centre of a previous scandal over political donations. In his memoirs, Mr von Brauchitsch writes of frequent visits from Dr Kohl's secretary, Julianne Weber.

"He would phone me from time to time and just say: Julianne is coming. Then she would explain to me that this or that local party organisation or protege of Kohl's needed support. She waited while I sent for the money," he recalls.

While Dr Kohl struggles to defend his reputation, his successor as chancellor, Gerhard Schroder, is relishing the Christian Democrats' discomfort. Already on the crest of a popular wave following his role in rescuing the construction giant, Holzmann, this week, the Chancellor is hoping that the sleaze allegations against his opponents will pay dividends for the government in two key state elections next year.

Dr Kohl's successor as Christian Democrats leader, Wolfgang Schauble, is attempting to distance himself from the party's past misdeeds. But as a lifelong Christian Democrat who owes his political career to Dr Kohl, Dr Schauble faces an uphill struggle in persuading the public that his party has changed.

As one disgruntled insider put it this week: "The problem is that the new Christian Democrats are also the old Christian Democrats."