For years they thought Paddy Hill was a mass-murderer who killed their loved-ones. Now the families of the 21 victims of the 1974 Birmingham pub bombings will stand with the Irishman as they learn if there is to be a new investigation in to the IRA killings.

A coroner in the Midlands city has signalled she will re-open an inquest in to the attacks adjourned more than 40 years ago after receiving what she called "significant" new information.

Those close to the case - including Hill - believe the breakthrough could be the revelation that there was a British informer in the IRA cell believed to have carried out the twin bombings at the Mulberry Bush and the Tavern in the Town bars.

Hill, the most vocal of the "Birmingham Six" men wrongly jailed for the crime after being tortured into confessing, said: "There was a mole. I am also quite sure that the Birmingham Police had information before the bombs went off."

Now based in Scotland, the 71-year-old has joined forces with the Justice4the21 group of relatives to get to the truth of what happened in the early evening of November 21, 1974.

Hill and five other Irish men were arrested within hours of the blasts killing 21 and injuring another 182. He admitted the crime after a gun was forced in to his mouth, smashing his teeth. He was jailed in 1975, and only released in 1991 when his conviction was quashed. Documents relating to the case have been sealed until 2069.

Hill and the families of the victims now both hope the inquest can bring some clarity. Speaking to the Sunday Herald, he said: "The police did a great job getting everyone to believe we were guilty. The families could focus on us being locked up. They just hated us for so long. Suddenly we got out and they started asking questions but the police stonewalled them. They have been told nothing.

"I have been working with some of the families for the last three years. The relationship is great. They realise the Birmingham police lied to them for 40 years."

Julie Hambleton of the Justice4the21 campaign - whose older sister Maxine died aged 18 in the Tavern in the Town, said: "It's already been a long journey. Whichever way it goes, it will continue to be a long struggle. All we want is the truth."

Hill, meanwhile, said he would "not be surprised" if an agent provocateur had been involved in the bombing. The bombings were a clear departure from IRA policy of focusing on military targets. Its command has said it would have sentenced anyone carrying out such an attack to death.

Asked about the bombings, he said: "It was a mistake for the IRA. You don't put bombs in civilian places. They were supposed to be at war with the British army, not the public."

Hill added: "I am angry at the British state because if they had done their job properly they would have caught the people who done it. They allowed the people who did it to get away scot-free.

"They either did that to protect their mole or they were not interested. I have no doubt in my own mind that the government, the judiciary and the police were complicit in the torture and framing of innocent people."

The IRA's then head of intelligence, meanwhile, believes reports of a mole are "very credible".

Kieran Conway, who ran the terrorist group's clandestine operations until 1975, said he had no first-hand knowledge that British security services had an informant in the Birmingham IRA, but said it had been happening in Northern Ireland at the time.

Conway - who is supporting the relatives of the victims and wants a full public inquiry - believes the bombings were an "absolute disaster" for the IRA.

He said: "The families should try to highlight the reports on security service pre-knowledge of the bombings."

The senior coroner for Birmingham will give a ruling on Wednesday on whether to hold new inquests.

Coroner Louise Hunt in February ordered West Midlands Police to hand over any information they had on a claim that British security services knew the attacks were going to happen.

Former Labour MP Chris Mullin, whose investigations helped free the Birmingham Six, said he "never came across any credible evidence" suggesting prior knowledge.