The killing of 14 civilians in Derry on Bloody Sunday in January 1972 was “unjustified”, Lord Saville's inquiry into the incident has concluded.

The inquiry's 5,000 page report was heavily critical of the behaviour of the British army in Derry on the day and found that all those killed were innocent.

The report states some of those who were killed or injured were clearly fleeing from the British paratroopers or going to the assistance of others who were dying.

The release of the report was greeted by loud cheers and applause by family members and their supporters gathering outside the Guildhall in Derry.

The inquiry concluded that several of the troops who provided testimony about the events lied to the inquiry and was particularly critical of one paratrooper regiment, which was deemed to have fired the 100 or so shots on the day.

Delivering the findings of the report, British prime minister David Cameron said it had found none of the casualties posed any threat to British troops. He told the House of Commons no warnings were given, and that some of the soldiers lost control.

“The Government is ultimately responsible for the conduct of the armed forces," he said. "And for that, on behalf of the Government, indeed on behalf of our country, I am deeply sorry.”

The report, completed over 12 years, investigated the mass killing of members of the Northern Ireland Civil Rights Association by members of the Parachute Regiment during a during a march in Derry on January 30th, 1972.

The men killed on the day were Patrick Doherty (32), Hugh Gilmour (17), Jackie Duddy (17), John Young (17), Kevin McElhinney (17), Michael Kelly (17), Gerald Donaghey (17), William Nash (19), Michael McDaid (20), Jim Wray (22), William McKinney (27) and Bernard "Barney" McGuigan (41).

John Johnston (59), one of the first to be shot on the day, died from his injuries four months later.

Lord Saville's report said the soldiers of the support company who went into the Bogside, where the march was taking place, did so “as a result of an order which should not have been given” by their commander. None of the casualties was carrying a firearm and while there was some shooting by IRA gunmen, “none of this firing provided any justification for the shooting of civilian casualties”, it found.

It concluded that “on balance” the first shot in the vicinity of the march was fired by British soldiers and no warning was given to civilians.

The support company “reacted by losing their self-control ... forgetting or ignoring their instructions and training” and the result was a “serious and widespread loss of fire discipline”.

The key finding were:

- “The firing by soldiers of 1 Para caused the deaths of 13 people and injury to a similar number, none of whom was posing a threat of causing death or serious injury.” This also applied to the 14th victim, who died later from injuries;

- “Despite the contrary evidence given by soldiers, we have concluded that none of them fired in response to attacks or threatened attacks by nail or petrol bombers.” The report added that no one threw, or threatened to throw, nail or petrol bombs at soldiers;

- The accounts of soldiers were rejected, with a number said to have “knowingly put forward false accounts”;

- Members of the official IRA fired a number of shots, though it was concluded it was the paratroopers who shot first on Bloody Sunday;

Lord Saville, who also investigated the activities of Provisional and Official IRA members on the day, concluded that Sinn Féin Deputy First Minister Martin McGuinness was probably armed with a Thompson sub-machine gun during the march, but that, although he may have fired the weapon, it was not possible to say so for certain. “He did not engage in any activity that provided any of the soldiers with any justification for opening fire.”

Later this afternoon the public is being asked to assemble at the Bloody Sunday memorial on Rossville Street in the Bogside and then to proceed to the Guildhall, symbolically breaking through Barrier 14 at William Street where the original anti-internment march was stopped and the shooting began.

An earlier inquiry into the events of the day by Lord Widgery was declared a whitewash and in 1998 British prime minister Tony Blair called for a fresh inquiry.

In the Widgery Report, Lord Widgery concluded “that there was no reason to suppose the soldiers would have opened fire if they had not been fired upon first”.

It said that while some soldiers showed a high degree of restraint in opening fire, the firing of others bordered on the reckless.

Lord Widgery said there would have been no deaths if those who had organised the illegal march had not, as this created a “highly dangerous situation in which a clash between demonstrators and the security forces was almost inevitable”.

The Saville inquiry is the longest in UK judicial history and had cost £190.3 million up to February this year. It sat at the Guildhall, Derry, and Central Hall at Westminster in London, to accommodate military witnesses.

About 2,500 people gave testimony, with 922 of these called to give oral evidence, including 505 civilians, nine experts and forensic scientists, 49 journalists, 245 military, 35 paramilitaries or former paramilitaries, 39 politicians and civil servants, seven priests and 33 Royal Ulster Constabulary officers.

Evidence ran to 160 volumes of data with an estimated 30 million words, 13 volumes of photographs, 121 audio tapes and 10 video tapes.

News organisations from the US, Italy, France, Russia, Nigeria, Australia and from the Middle East have gathered in Derry to hear details of the incident, as well as journalists from Ireland and Britain.