Fines issued under Victoria's myki system have never been contested in court, amid claims the government has been forced to waive infringement notices because the troubled technology cannot withstand legal scrutiny.

The Department of Transport, Planning and Local Infrastructure has been warned by staff that a successful legal challenge could undermine the integrity of the $1.5 billion ticketing system, which has operated for more than three years.

Illustration: Matt Golding.

A former contractor said he provided the department with verbal and written advice that false readings, administrative errors and poor calibration of machines would damage the chances of a prosecution in court.

''They [the transport department] don't want it to be tested in court, they just want the revenue. They need to prove beyond reasonable doubt and they simply can't. I know of several cases where people have challenged infringement notices on the basis of faulty technology, but the prosecution has withdrawn the fines,'' the source said. ''As a prosecutor, you have an ethical duty to the court and I would regularly explain to them that this system won't stand up to scrutiny.''