Chris Mullin, the journalist, justice campaigner and former Labour MP, has responded to criticism from families of victims of the 1974 Birmingham bombings, saying the names of suspected bombers were known to them only because of his investigations.

Mullin, whose investigative work helped to exonerate the Birmingham Six, was angrily denounced by some bereaved relatives when he refused to name any of the still-living suspected bombers while giving evidence at the recent inquest into the atrocities.

He has maintained that journalistic ethics have precluded him from naming the suspects, having given assurances that he would not disclose the identities of IRA members he interviewed in the past.

But Julie Hambleton, who lost her older sister in the bombings, said after the end of the six-week inquest on Friday that “the first port of call” for any new official inquiry into the bombing should be Mullin, whom she accused of obstructing previous police investigations.

Mullin, who was confronted by some relatives while leaving Birmingham civil justice centre last month, told the Guardian: “Far from obstructing justice, I am the person who helped clear up the mess and it would be nice if some of those concerned could bring themselves to acknowledge that.”

The convictions of six innocent men over the bombings, one of the British legal system’s gravest miscarriages of justice, were quashed in 1991 after years of campaigning by their families, supporters and others.

Mullin initially investigated the case for Granada TV and wrote a 1986 book setting out a detailed case supporting the men’s claims. He said: “No one was doing any investigating when I came on the scene; indeed much of Birmingham was in denial and remained so until relatively recently.”

As part of this, he said he tracked down and interviewed 16 or 17 people who had been planting IRA bombs in and around Birmingham.

“In order to track down the bombers, I had to give assurances not only to guilty but to innocent intermediaries that I would not, during their lifetime, disclose the names of those who cooperated. Had I not done so, no one would have cooperated,” he said.

On Friday, relatives of the 21 people killed in the 1974 bombings urged police in Britain and Ireland to bring the alleged perpetrators to justice after an inquest ruled the victims had been unlawfully killed.

The plea was made at the end of a hearing that resulted in a jury ruling that a botched warning call in advance of the attacks caused or contributed to the deaths.

Seizing on the evidence of a convicted IRA bomber, who named four men as being responsible for the attacks, relatives demanded that police launch fresh criminal investigations and charge living suspects with what was now officially known as murder.