The long-awaited inquests into the deaths of 21 people in the 1974 IRA Birmingham pub bombings have begun with a minute's silence for the victims.

Coroner Peter Thornton told jurors they would hear evidence of how the bomb blasts ripped apart two pubs on what was a "perfectly ordinary evening" in Birmingham.

The 11 jurors - six women and five men - were also told that the inquests could last up to six weeks.

Mr Thornton said: "You have a duty, as citizens, to sit in courts of this country on a jury when summonsed and it is an important civic duty."

Three reserve jurors have also been sworn in.

Coroner Peter Thornton

The coroner said there would be evidence alleging British security forces may have had some forewarning about the attacks, widely thought to have been carried out by the provisional IRA, including an "overheard" conversation which took place in prison two weeks before the bombings.

The inquests will answer many questions, but will not address the key issue of who planted the bombs. The coroner has said that is beyond the scope of the inquests, saying that it was a "task of police, prosecutors and the criminal courts".

That decision angered relatives of those who were killed, but they say it would be an insult to the victims not to take part in the proceedings.

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The inquests, which are being held in Birmingham, are the culmination of years of campaigning by relatives of the dead for a full account into the circumstances of what happened on the night of 21 November 1974.

The IRA bombings of the Mulberry Bush and Tavern in the Town pubs was the deadliest post-World War II attack on the British mainland, until the 7 July London blasts in 2005.

A botched investigation by West Midlands Police led to the convictions of the Birmingham Six, who were found guilty of the murders a year later.

But their convictions were quashed by the Court of Appeal in 1991, after the men had spent 16 years behind bars.

As well as those killed, 220 were injured in the blasts, which were carried out at the height of an IRA bombing campaign in the West Midlands, the jury was told.

A third bomb, jurors heard, was planted near the Barclays Bank on the Hagley Road but failed to properly detonate that night.

The coroner said that there had been "over 50" incidents involving bombs and incendiaries "in and around Birmingham" in 1973 and 1974, but that after the pub blasts "the campaign in the West Midlands stopped".

He told the six women and five men of the jury it would be a matter for them whether the IRA called off its Midlands campaign because of the "outrage of civilian deaths on this scale" or "some other reason".

The coroner said: "This is something that the city of Birmingham has suffered now for many years.

"While the inquests will inevitably focus on those who died we must also remember many other lives were and continue to be affected."

Jurors, sitting at Birmingham Civil Justice Centre, were told they would hear evidence from only a few eyewitnesses of those there on the evening, because some were "no longer alive".

He added: "They will be doing their best to recollect events accurately, but we all know memory will sometimes have gaps.

"Recollection may sometimes be distorted or inaccurate, it may be correct."

The coroner said "nobody has been successfully prosecuted for the attack", and that the only men ever to stand trial, the Birmingham Six, were freed on appeal in 1991.

He also said: "Nobody is on trial here, an inquest does not decide matters of criminal or civil liability, and this is not a question of attributing blame to any individuals."

He told jurors who "may well be wondering why now", that the original inquests were put aside in 1975, with the start of the six men's criminal trial.

The former chief coroner for England and Wales added that there would be details of the so-called "forewarning issue", and evidence the British authorities may have received information signalling there were to be bomb attacks.

Among them, evidence of an alleged tip-off concerning a "possible conversation in a local prison nearly two weeks before the bombings".

Jurors would also hear an account of "evidence of a students' visit to a police station the evening of the bombings, which was cancelled".

Detailing the chain of events that night, the coroner said that at 8.11pm, the Birmingham Post and Mail newspaper received a coded bomb warning from a man "with an Irish accent" accompanied with the code word "double X".

The caller, ringing from a telephone box, spoke of a bomb in the city's landmark Rotunda, and the tax office in New Street.

The coroner said that the newspaper's telephonist's record of the message made no mention of pubs.

The two bombs detonated in "massive explosions" between 8.15pm and 8.20pm, killing 19 on the night - eight in the Mulberry Bush, at the foot of the rotunda, and two outside the nightspot.

Another nine died in the Tavern In The Town, which was a large pub in the basement of the same building as the tax office, King Edward's House.

Two died later of their injuries, with 12 of the victims under 25.

The coroner Mr Thornton said: "It was a normal Thursday evening in Birmingham, on November 21, 1974.

"It was not a weekend, but the pubs, two in particular, were busy enough and both quite popular with young people."

He added the premises were only some 50 yards away from one another.

"At 8pm that evening, it was a perfectly ordinary evening in the two pubs, a film was showing at the Odeon cinema but just after 8.15pm, all of that changed.

"Moments later there was an explosion at the Mulberry Bush, and just minutes later a second explosion at the Tavern In The Town.

"They were massive explosions."

He told jurors: "After hearing the evidence you may conclude the bombs were brought and planted in such a way that extensive loss of life, injury and devastation, would have been caused.

"They were planted in enclosed spaces in busy pubs, where there were many people.

"You may be asked to determine whether those who died were unlawfully killed."

Hearings will continue on Tuesday and Wednesday with pen portraits of each of the victims, while on Thursday, the jurors will be taken to the former sites of the pubs - both since long gone.

The inquests, which are being held in Birmingham, are the culmination of years of campaigning by relatives of the dead for a full account into the circumstances of what happened on the night of November 21, 1974.

Mr Thornton previously ruled that the hearings will be Article 2 inquests, examining whether the British state or its agents failed to adequately protect the victims.

Julie Hambleton, whose 18-year-old sister Maxine was among those killed, attended the inquest, alongside some 15 other bereaved family members.

She has said previously that all the bereaved were seeking was "truth, justice and accountability".

Jayne, Julie and Brian Hambleton, who lost their sister Maxine in the bombings

Additional reporting: PA