However a victims advocate says the decision of hostages to publicise their ordeal, and receive payment, is a personal one and should be respected.

Mr Kennett, who is also the founder of Beyond Blue, an organisation that raises awareness of anxiety and depression, took to Twitter on Monday night to criticise reports that hostages have been paid large sums in exchange for their inside accounts of the Lindt café siege at Martin Place last month.

"Is it not sad [that] those involved in the Sydney siege, who's [sic] lives were saved are now selling their stories for profit. Terribly disappointing," Mr Kennett wrote.

"One survivor is alleged to [be] being paid $400,000. What for, being in the wrong spot at the wrong time. To be rescued by others who put their lives on the line. Give me a break!"

Mr Kennett said huge sums of money were spent ending the siege, and the hostages owed their lives to "the brave acts of others".

"Many first responders put their lives at risk. Two innocent hostages lost their lives. I do not think it is morally right that the media pay, and [that] any of those who were saved should profit from the attack," he said, describing the payments as "just plain grubby".

News Corp has reported that siege survivor Marcia Mikhael has been signed by Channel Seven for $400,000, while John O'Brien will be paid $100,000. However, Fairfax Media understands the real amounts are substantially lower. A lawyer for Ms Mikhael declined to comment on Mr Kennett's remarks, or the reported figure.

Meanwhile, Nine is rumoured to have signed four Lindt cafe workers – Fiona Ma, Harriette Denny, Joel Herat and Jarrod Morton Hoffman – for a combined $1 million, though Fairfax Media understands this figure may not be accurate.

Many Twitter users took exception to the comments.

User "dennis michael" said it was surprising that Mr Kennett had "no compassion [for the] victims of trauma. Real eye opener".

One user who goes by the name "george" told Mr Kennett that he agreed with him in principle, but "not everyone is as financially comfortable as you are".

However others on Twitter backed Mr Kennett's views. Patrick Lyttleton said the payments to hostages were "disrespectful to the deceased", adding "their reward is surviving".

Ramsay Yamak noted that emergency services workers involved in the siege "will only take home their yearly wage".

Mr Kennett later told 2UE radio that the hostages had gone through a terrible ordeal, and it was important they talk about their experiences to aid their recovery.

But he said the hostages were likely to receive compensation and the payments were "ghoulish".

"Ghoulish by the media, ghoulish by those who are either demanding or accepting payment. They have their lives. Yes, they have been through a traumatic circumstance, but some of them actually may be alive because of the actions of [fellow hostage and victim] Tori Johnson. Some of them may be alive because of the act of our police men and women," Mr Kennett said.

"I think it is inappropriate, I think it is insensitive, I think it is wrong that the money was offered, I think it is wrong that the money is accepted."

However victims of crime advocate Howard Brown said accepting payment was "a personal decision made by each individual hostage".

"The fact that some of the hostages feel comfortable with selling their story doesn't mean that all the hostages will feel comfortable selling their story ... we have to respect each hostage's rights to make a decision one way or the other," he said.

"For some of these hostages, giving the interview will be a cathartic process for them."

Mr Brown said while he appreciated Mr Kennett's point, "he has never been a hostage; he cannot get inside their mind".

A spokeswoman for Justice NSW, a government agency that runs a victims support service, says any decision to sell a story was "a personal matter for victims to decide".

She said support for those directly affected by the Sydney siege has included free and unlimited trauma counselling, replacement of mobile phones and financial assistance to help their family members travel to Sydney.

Mr Kennett's controversial remarks follow comments by NSW Christian Democrats MP Fred Nile, who last week said the male hostages who fled the siege did not deserve bravery awards.