The broadcaster Ray Hadley has criticised former Liberal prime ministers John Howard and Tony Abbott for expressing sympathy with George Pell, warning that to doubt the verdict is to call the cardinal’s victim a liar.

The conservative broadcaster told 2GB Radio on Thursday Howard had gone “way over the top” by providing a “gushing reference”.

“It’s my opinion Mr Abbott and Mr Howard have made gross errors of judgment,” Hadley said, noting that paedophiles escaped punishment because they hid their crimes and “con their friends and colleagues”.

“This is not over, there is an appeal process. For someone as prominent as Mr Howard to basically say the victim’s a liar and Pell’s not, is not what it should be about.”

On Thursday morning the head of a child sexual abuse legal service also condemned columnists who have expressed their disbelief in the verdict, warning it sends an “incredibly damaging message to survivors”.

Warren Strange, the executive officer of Knowmore legal service, told a parliamentary inquiry he expected the “unprecedented” publicity around the Pell case to drive a spike in claims but media commentary doubting the verdict might deter victims from seeking justice.

After Pell’s conviction, revealed on Tuesday, of one count of sexual penetration and four counts of indecent assault against two 13-year-old choirboys, several commentators including News Corp’s Miranda Devine and Andrew Bolt declared their belief in Pell’s innocence.

Pell has also been defended by Howard, in a glowing character reference labelling him a “person of both high intelligence and exemplary character”. Abbott has revealed he called Pell after the verdict and indirectly supported him by continuing to call the cardinal his friend.

On Thursday a parliamentary joint committee met in Canberra to hear evidence on the effectiveness of the victims’ redress scheme set up after the institutional child sexual abuse royal commission.

Strange told the hearing that Knowmore had already seen “a number people contacting us across the last couple of days as the result” of the Pell case, explaining they were “not just survivors who experience abuse in a Catholic institution, it can elevate survivors from any context”.

“I expect there will be an impact. Certainly whenever there is that level of attention – and this [case] is perhaps unprecedented – whenever there has been significant media attention we tend to see a spike in calls,” he said.

Senator Derryn Hinch suggested that particular media articles doubting the verdict could deter victims, citing the fact that many do not come forward because they fear they will not be believed.

Strange said that he is “deeply concerned” about those articles, accusing commentators of “attempting to traverse the verdict of the jury who had the benefit of sitting in court and hearing all the evidence”.

“And with due respect to those columnists, the defence team for the particular accused was better able to point to all the circumstances and to argue the case for an acquittal – and that didn’t happen, the jury’s verdict has come in,” he said.

“To then say I don’t believe it, or it’s wrong, I think that sends an incredibly damaging message to survivors who are thinking about coming forward.

“They must be thinking, some of them will be thinking ‘why would I do this, why would I put myself through a process like that then run the risk of public criticism’ for an outcome we’ve seen.

“I think it can potentially be very, very damaging to survivors to be writing those types of stories.”

Hinch also took aim at defence barrister Robert Richter’s submissions in relation to sentencing that Pell’s offences were “plain vanilla offending”, labelling it “absolutely offensive”.

Strange suggested that measuring sexual assault by metrics such as the duration of the offence is “devastating for survivors”.

“They don’t see things through the same lens, that [conduct is] not at the worst possible scale of offending – it’s irrelevant to them.”

Strange told the hearing that one cause of the delay in claims is that some “major institutions” have yet to join.

The department of social services has started to publish a list of institutions that are yet to join the redress scheme. Currently there are more than 100 organisations which were named in the royal commission that are yet to join.

The social services minister Paul Fletcher said the decision to name the institutions will provide transparency for abuse survivors considering applying for redress payments, but the government also expects those not named in the royal commission to join.

Departmental officials told the hearing the majority of institutions had now responded giving a timeframe to join the scheme but some had not received the initiative to name and shame them well.

It was last week revealed 51 Australians have received payments through the scheme, receiving on average $79,035. Officials blamed delays on many institutions only joining the scheme in December.