The Revenue Commissioners has initiated contact with Ansbacher Cayman in pursuit of tax arrears. The amount involved could be up to €100 million, according to one source.

A spokesman for the Ansbacher group said its Cayman subsidiary had received "tax returns" from the Irish Revenue but no demand for any payment.

He said no provision for any payment had been made in the books of the FirstRand Corporation, the publicly-quoted South African company that now owns the Henry Ansbacher group.

"It is not expected that there will be any liability, so there is no provision made in the accounts," the spokesman said.

He said the bank was taking expert advice on the matter. A note in the corporation's accounts refers to the Irish inquiry but says it does not expect any liability to arise.

The returns sent to the Cayman bank are to allow it declare annual liabilities arising from its activities here going back to the early 1970s.

A spokesman for the Revenue said it did not comment on individual cases but was pursuing all Revenue aspects detailed in the Ansbacher inspectors' report and information arising from its own investigations.

The Ansbacher inspectors' report, which was published last year, found that Ansbacher had established business in Dublin in Guinness & Mahon and later in the premises of Cement Roadstone.

It also found that there was evidence "tending to show" that Ansbacher failed to pay corporation tax lawfully due.

Furthermore, it is understood that, under Section 31 of the Finance Act, 1974, the bank may have had an obligation to withhold some of the annual interest it paid to its Irish customers.

Because the Cayman bank was not registered here as a bank, it did not have to collect DIRT on its Irish accounts. However, all non-bank companies that pay annual interest to third parties are required to retain some of the interest paid as retention tax at the standard rate.

The Guinness & Mahon subsidiary, Guinness Mahon Cayman Trust, was found by the inspectors to have carried on business here since the early 1970s.

In the late 1980s it was bought by the London-based Henry Ansbacher group, which was in turn bought by First National Bank of South Africa in 1993. First National is now part of FirstRand.

Although the FirstRand group had no connection with the Irish operation run by the late Mr Des Traynor for most of the time during which that operation was active, it nonetheless took on the debts of the Ansbacher group when it purchased it.

Any taxes due to the Irish Revenue as a result of Ansbacher's activities here would inevitably incur interest and penalties. The interest would date from the 1970s.

An obvious difficulty which would arise for the Revenue is that it cannot enforce any assessment which might arise, as Ansbacher Cayman has no operations in this jurisdiction.

The Revenue is already involved in a huge trawl through the affairs of the clients identified in the Ansbacher inspectors' report with a view to raising assessments against people and companies that may have used the Cayman bank to evade tax.

It is understood that many of the clients are resisting the Revenue's contention that they have a tax liability.