Prison sentences should be increased for drugs users convicted of possession and who fail to inform gardaí who supplied them, a former Criminal Assets Bureau legal officer has said.

Barry Galvin told the meeting of the Irish Association of Former Parliamentarians that such a move would be a form of deterrent but it would be a “huge advantage to the gardaí” as an investigating tool.

Mr Galvin said in the course of interviewing a citizen caught with heroin, gardaí should be able to ask him (or her) – on pain of criminal offence for failure to reply – “Where did you get the heroin?”

He said the only time gardaí got the information was from video “because there is a culture of omerta, a built-in fear”.

Mr Galvin said that if a drug user refused to reveal their supplier, after they received their sentence for possession, they would then be tried for failure to assist. “That should be a serious offence and should be consecutive to the original offence,” he said.

“There is going to be an inherent fear factor. In reality everyone can’t be afraid,” gardaí would get huge information and it would be of major assistance “in dealing with the higher lads”.

Former minister for justice Dermot Ahern said that during his time as minister, “the event that really changed everything was the murder of Roy Collins in 2009”. He was the son of a man who had given evidence against ganglords and was killed for that reason.

Mr Ahern said it was an attack on society, the State and its institutions. “We had to take out of the equation as much as possible the civilian witnesses” and laws were introduced that created certain offences and transferred the trial of organised crime offences to the Special Criminal Court, Mr Ahern added.