Des Traynor's political connections to Charles Haughey have been well documented. But for months now the Tanaiste, Ms Harney, has been muttering darkly that the Ansbacher depositors, the fund from which Mr Haughey's bills were paid, also included some of the biggest names in Irish business.

Yesterday came the proof. Irish companies don't come any bigger than CRH. Of the 15 people on CRH's board of directors in 1987, eight were the beneficiaries of Ansbacher deposits, according to an affidavit presented in the High Court by a senior official of the Tanaiste. It goes on to point out that "this strongly suggests that a substantial number of the directors knew that an unlicensed bank was operating from its registered office". And was operated by the company's chairman, Des Traynor.

There has been much speculation over the past year or two about how the Ansbacher deposits operated and the identity of the beneficiaries.

The information set before the court yesterday fills in many of the gaps and suggests a tax evasion operation larger than previously uncovered and operating in a very sophisticated way.

At its very heart was Des Traynor and many of those who availed of the Ansbacher services are likely to turn out to be his friends and business associates.

The Ansbacher accounts might never have come to light but for a name on a cheque written by Ben Dunne. Des Traynor arranged for Mr Dunne to route payments to Charles Haughey through John Furze. Mr Furze, who died in 1997, worked for Guinness & Mahon and Ansbacher in the Cayman Islands.

This provided the crucial link for the investigators from the McCracken tribunal, who discovered that the money was routed back into an account held by the Cayman Islands bank in Guinness & Mahon in Dublin, the bank where Des Traynor was deputy chairman for many years. And, by the way, the McCracken team mentioned in passing, these accounts totalled as much as £38 million and appeared also to have been used by many other Irish individuals to evade tax.

Now we know at least £50 million was involved - and possibly much, much more - and three High Court inspectors are to investigate the affairs of Ansbacher (Cayman) in Ireland.

The business of the bank was operated in a very sophisticated way by Mr Traynor but the essence of the schemes it used were simple enough. Depositors - keen to hide money from the Revenue Commissioners - routed their funds offshore to Ansbacher (Cayman). Some did so by establishing discretionary trusts, managed by Ansbacher on their behalf. For other account-holders, the bank deposited funds in the Irish banking system in its name and Mr Traynor ensured they could make withdrawals as they wished.

No record of the depositor's name was held in the Irish banks holding the money - Guiness & Mahon and later Irish Intercontinental Bank.

As a further service, Mr Traynor arranged loans for Irish people, using the money contained in the Ansbacher deposits as security. The Irish banks lending the money kindly agreed with Mr Traynor not to write on any documents the home of the funds being used to guarantee the loans.

This system of so-called back-to-back loans added another twist to the tax evasion, it emerged in court. It allowed those with money hidden offshore - thus presumably avoiding income and capital acquisition taxes - to borrow on the strength of these deposits. Their Irish companies, to which the loans were extended, could then benefit by treating the interest on these loans as a deductible expense, thus cutting their corporation tax bills.

The affidavit identifies a number of companies which benefited from these back-to-back loans. Two companies - Carlisle Trust and Alstead Securities - borrowed £17.5 million sterling during the 1990s.

Carlisle Trust is the principal vehicle of Des Traynor's friend and associate, property developer John Byrne, and he is also associated with Alstead. Byrne, like Traynor, was close to Charles Haughey and a number of payments from donors to Celtic Helicopters, run by Mr Haughey's son, Ciaran, were routed through Carlisle Trust.

A £1.88 million loan was also extended earlier - in 1998 - to Dublin estate agent John Finnegan, who ran the Finnegan Menton company.

And bringing it back to the Haughey family, the affidavit reveals that Des Traynor intervened to change the wording of a facility letter from IIB to Conor Haughey - another son of Charles Haughey - and his wife Jacqueline, which agreed to provide a £60,000 guarantee in favour of Bank of Ireland in respect of overdraft facilities.

The original letter from IIB mentioned deposits in the bank as providing the guarantee but Mr Traynor got this deleted, lest anyone ask: "What deposits?"

It was typical of the careful steps which were taken in many parts of the Ansbacher operation to avoid detection by tax officials or auditors. Intriguingly, details of correspondence between Mr Traynor and an unnamed senior figure in the Irish financial community titled "Towards Minimising the Fooprints" are included in the affidavit.

The overall picture is of a tax evasion scheme of extraordinary breadth and complexity. The court document raises the estimate of the amount of funds held in the Ansbacher deposits from £38 million to £50 million, held by more than 100 beneficiaries.

But it also points out that Ansbacher (Cayman) ran other services for wealthy Irish individuals, including the establishment of offshore trusts and companies.

The sworn affidavit goes on to state that the sum of money involved in these trusts and companies may amount to several hundreds of millions of pounds.

So it appears that the Ansbacher deposits themselves were just the tip of a massive tax evasion iceberg. If this is correct it brings the activity of Ansbacher (Cayman) in Ireland on to an entirely new level and this will surely be a priority area of investigation for the High Court inspectors.

The Revenue clearly lost substantial sums of money. But everyone else gained. Ansbacher (Cayman) - like any bank - took a margin on the deposits and loans.

The depositors hid money from the Revenue and had easy access to their funds. And the two agents in Ireland - Des Traynor and accountant Padraig Collery - earned substantial fee income from the business "which was paid to them without any evident deduction of tax by being credited to their personal accounts in the memorandum accounts". Mr Collery told the inspector that he had almost £500,000 in deposits.

While the deposits continued for a while after his death, it is clear that Des Traynor was the central figure in the entire arrangement. He used them to channel money to his political friend, Charles Haughey, and to hide the money of his business friends and associates from the tax authorities.

If the inspectors discover that the sums salted away by Ansbacher (Cayman) on behalf of Irish tax-dodgers did run into hundreds of million of pounds, then the scale of the mini-empire he built will have been even greater than we thought.