Guido has been given documents coming from inside Anglo Irish Bankís Treasury Department dating back to 1997 which strongly suggest there was a board level approved conspiracy to over-charge corporate customers. The scale of the fraud was massive and it may have contributed up to 10% of the now nationalised bankís profits.
The Anglo-Irish Bankís fraud comes from overstating the DIBOR base rate on which customerís loans were calculated. DIBOR is the Dublin Interbank Offered Rate calculated and was published daily like LIBOR, it is set in stone and used by all Irish banks as the basis for settlement of trades and financial transactions before they joined the Euro.
Essentially Anglo-Irish lied to customers as to what that the real base rate was by adding between 1/4% to 1/3% to the official underlying rate, then they added the usual bankerís spread that they will have agreed contractually with their corporate customers.