Germany's opposition Christian Democrats started using secret accounts to disguise illegal donations before 1971, the party revealed yesterday after a meeting of its leadership in Bonn.
The party's former financial adviser Mr Horst Weyrauch told an internal inquiry that millions of pounds were channelled through accounts in Switzerland and Luxembourg before being taken back to Germany in cash for use in election campaigns.
"We have made a series of new and painful discoveries," the party leader, Dr Wolfgang Schauble, said.
But the party failed to discover the identity of donors who gave the former chancellor, Dr Helmut Kohl, almost £1 million between 1993 and 1998. Former aides revealed, however, that Dr Kohl received a similar sum in cash between 1989 and 1992 which he did not declare in official party accounts.
Dr Kohl refused to identify the donors when he was questioned by the party on Thursday, but he denied that one of those who gave him cash was the media magnate Mr Leo Kirsch.
Party officials questioned three key figures who had responsibility for party finances over the past 30 years and, although their testimony was sometimes contradictory, a clear picture of systematic illegal funding practices emerged.
One former official, Mr Uwe Luthje, claimed that the electronics group Siemens gave the party £400,000 in the late 1980s or early 1990s. But the company insisted that there was no evidence of such a payment.
Siemens paid over monies to the CDU via company director Mr Wolfgang Seelig, party secretary general Mr Willi Hausmann told a news conference yesterday.
Some donations were deposited in a Zurich bank account and others brought into Germany in cash to be put into secret CDU bank accounts, according to Mr Luthje's affidavit.
Siemens, asked by CDU officials about the contributions, said it "had no means of confirming that these payments had taken place", Mr Hausmann said.
In a press statement sent from its Munich base, Siemens repeated this line, but added that the group would "do all it could to shed light on this affair".
The firm said that Mr Seelig had ceased to be a Siemens board member on September 30th, 1984, and that he had left the firm in 1986 after two years acting in a purely advisory capacity.
"Mr Seelig told us he had never given money to Luthje," Siemens said.
Former party treasurer Mr Walter Kiep, questioned by the CDU, also denied Mr Luthje's allegations, claiming he had never received money from Siemens in Switzerland, Mr Hausmann said.
The party leadership has rallied around Dr Schauble, who has been accused of giving a misleading account of his receipt of £40,000 from a fugitive arms dealer.
All the witnesses the party questioned backed Dr Schauble's version of the transaction and his colleagues insisted that his position as leader is secure.
Dr Schauble expressed regret that Dr Kohl had failed to name the donors of illegal funds and said he would pass on to state prosecutors all information the party has discovered.
Prosecutors are investigating Dr Kohl on a possible charge of misusing party funds. The former chancellor resigned as honorary chairman of the Christian Democrats last month but he has defied calls to give up his seat in parliament and leave political life for good.
Meanwhile, a clear majority of Germans believe Dr Schauble should resign over the financing scandal, according to a poll published yesterday.
A Forsa poll for N24 television found that even among CDU supporters, 55 per cent believed the party leader should resign, while among the population as whole the figure was 63 per cent.
