In the most dramatic development yet in the prosecution of eight allegedly corrupt Australian executives, Radius Christanto, pictured, has made a secret deal with the Australian government to plead guilty to bribery and testify in a Victorian court.

A senior government source told Fairfax that in return for his co-operation Christanto is likely to get a greatly reduced jail term.

The deal is significant because Christanto will provide the first explicit, first-person witness testimony about the way the RBA bank-note firms Securency and Note Printing Australia allegedly used middlemen to funnel multi-million dollar bribes to overseas officials in return for securing their agreement to purchase Australian polymer bank note technology.

It's understood the testimony of Christanto - a millionaire businessman who conducts much of his business on exclusive Asian golf courses - may not only implicate several of the already charged Australian bank note executives, but lead to fresh charges in Australia and Britain.

His testimony also has the potential to implicate four former top Indonesian central bank officials who allegedly received the huge bribes.

Along with testifying about the alleged role of the RBA bank note executives in the bribery scheme, prosecutors expect him to verify the authenticity of faxes sent between him and Securency and NPA and which contain explicit references to alleged bribes.

In the faxes, Christanto allegedly describes certain senior Indonesian central bank officials as ''our friends'' who expect to be given huge ''unofficial payments'' and ''commissions''.

In a fax sent to a Securency executive on July 1, 1999, Christanto, who represented the RBA firms in Indonesia between 1999 and 2006, allegedly stated:

''Please kindly understand my difficult position because it involves a very huge amount of money which have been committed to our friends.''

Another fax allegedly refers to the Indonesian central bank officials as '' … being high-ranking officers … They did ask the big amount up-front''.

Mr Christanto helped win the RBA firms a 1999 contract to print 500 million 100,000-rupiah banknotes for Bank Indonesia. The contract was worth more than $US50 million to the RBA firms.

According to Mr Christanto's correspondence he was to receive a $US3.65 million commission from Securency/NPA in a Singapore bank account after he helped win the 1999 Bank Indonesia contract.

His faxes also allegedly indicate two figures, ''Mr S'' and ''Mr M'', were to receive $US1.3 million in alleged bribe payments from the RBA firms.

Mr Christanto's faxes with the RBA firms also reveal alleged collusion between Bank Indonesia officials, Mr Christanto and RBA banknote executives to ''mark up'' the Securency/NPA bid for the rupiah banknote contract by 20 per cent with an agreement that it would then be reduced to a 10 per cent mark-up.

Securency is half-owned by the RBA and makes polymer substrate for banknotes used in nearly 30 countries.

NPA is wholly owned by the RBA and prints Australia's polymer currency.