Former federal MP Craig Thomson will face more charges as prosecutors attempt to clarify the details of his alleged misuse of union credit cards.

Thomson, 49, is accused of misusing credit cards to pay for female escorts and X-rated movies while he was national secretary of the Health Services Union (HSU) and a Labor MP.

Prosecutor Lesley Taylor SC told the Melbourne Magistrates Court on Tuesday that about 50 new charges would be lodged against Thomson, after his lawyers complained of duplicity within the existing 173 charges.

Thomson is charged with 11 counts of theft, 31 counts of obtaining property by deception and 131 counts of obtaining a financial advantage by deception.

Ms Taylor said there was no new criminality alleged against Thomson.

In most of the charges the alleged victim was the HSU, she said.

“He is deceiving the union by saying that this transaction is a union expense and not a personal expense,” she told the court.

However, Thomson’s barrister Greg James QC said the structure of the case against his client meant it was “doomed to failure”.

Ms Taylor said negotiations between prosecutors and Mr James will continue before the matter returns to court on Monday, when the hearing is scheduled to start.

Magistrate Charles Rozencwajg extended Thomson’s bail until Monday.