Six armed Iranians overpowered police constable Trevor Lock, of the diplomatic protection squad, who was standing guard outside the embassy. Inside the building they took 26 hostages.

Hostages released

Frieda Mozafarian: Released on 1st day Chris Cramer: Released on 2nd day Ali Guil Ghanzafar: Released on 4th day Hiyech Sanei Kanji: Released on 4th day Mustapha Karkouti: Released on 5th day Abbas Lavasani

It ended five days later when the SAS stormed the embassy and killed five of the gunmen.

The siege was played out in the full glare of publicity. The final drama unfolded in front of millions of viewers, the pictures relayed live by TV cameras during peak time on Bank Holiday Monday.

Shopping list

Hostages freed by SAS

Dr Gholam Ali Afrouz: Wounded Akmed Dadgar: Wounded Dr Abul Fazi Ezzati Abbas Fallahi Muhammad Hashir Faruqi Simeon Harris Nooshin Hashemenian Roya Kaghachi Vahid Khabaz Shirazed Bouroumand PC Trevor Lock Moutaba Mehrnavard Aboutaleb Jishverdi-Moghaddam Muhammed Moheb Ronald Morris Issa Naghizadeh Ali Aghar Tabatabai Kaujouri Muhammed Taghi Zahra Zomorrodian

The six Iranian gunmen claimed to be members of a minority Arab population in southern Iran. They called themselves the Democratic Revolutionary Front for Arabistan - their name for the oil-rich Iranian province of Khuzestan.

They were protesting against oppression by the Ayatollah Khomeini who had come to power in Iran during the previous year.

The hostages were mainly Iranian embassy staff, but also included a number of tourists and two BBC employees - journalist Chris Cramer and sound recordist Sim Harris - who had stopped by to pick up visas.

Later that day Mr Cramer telexed a shopping list of demands to the police from inside the embassy.

Pro and anti Khomeini protesters gathered outside

The gunmen wanted the release of 91 political prisoners who were jailed in Iran and a plane to fly themselves and the hostages out of the UK. They also wanted negotiations to be carried out by ambassadors from Iraq, Jordan and Algeria.

If their demands were not met the gunmen threatened to execute all the hostages and blow up the embassy.

SAS alert

The Special Air Service - the counter-terrorist regiment known as the SAS - was immediately put on standby. It studied plans of the building, attempted to install listening devices in the walls and drew up a plan to free the hostages.

Police controlled the gathering crowds

A ministerial and civil service committee, headed by the Home Secretary William Whitelaw, was also brought into action to deal with the national emergency. It was named Cobra - after the Cabinet Office briefing room - the location of its meetings.

Trained police negotiators attempted to calm the gunmen, reassuring them that many of their demands would be met.

The hostage-takers were led by 27-year-old Oan, codenamed Salim, who was the only one who spoke English.

Over the next few days he apologised for the "trouble" they were causing and also released a number of hostages. On the first day a woman hostage was freed and on the second Mr Cramer was released having complained about a severe stomach illness.

Hundreds of journalists, TV crews and photographers set up outside

By the third day the gunmen had become cagey - not convinced that their demands were getting through.

By this time Cobra had already decided not to provide the plane and although officials were in talks with a Jordanian diplomat, they had also decided not to involve an Arab ambassador.

On Saturday the gunmen released two more hostages, including a pregnant woman. On Sunday another hostage was released. But by Monday the mood had turned ugly.

Tension rises

At 11am Pc Trevor Lock told the police through an open window that one of the hostages would be shot if there was no firm news about the ambassador within 30 minutes. The police responded that talks were in progress.

Iranian hostage Abbas Lavasani was tied up separately on the ground floor - most of the other hostages were under guard on the second floor.

Hostage Pc Trevor Lock was hailed a hero after the siege

Mr Lavasani, a keen supporter of Khomeini, was heard to argue with the gunmen on several occasions. Three shots were heard at about noon. Abbas Lavasani was shot dead, although it was unclear whether he died then or some hours later when more shots were fired.

Mr Lavasani's body was pushed out a door of the embassy in the early evening. The death of a hostage meant that the siege would now be brought to an end - by force.

Operation Nimrod

The SAS went in barely 20 minutes later - their assault relayed by TV cameras trained on the embassy. In 15 minutes it was all over.

Fire caused by the SAS grenades took hold of the building

Operation Nimrod was widely regarded as a success. Pc Lock was hailed a hero - he had tackled "Salim" - real name Awn Ali Mohammed - the leader of the gunmen, saving the life of an SAS man. He was later awarded the George Cross for his actions.

The siege ended with two hostages dead and one of the gunmen left alive.

Prime Minister Margaret Thatcher said the performance of the SAS was "superb" and they made everyone "proud to be British".

Mr Whitelaw said he regretted force had to be used - but that there was "no alternative".

Iran also welcomed the end of the siege and declared the hostages that had been killed martyrs.

With its operation played out in front of the TV cameras, the SAS's expertise was now firmly established. The future of the regiment, previously threatened with disbandment, was now guaranteed.

But once the sense of euphoria had worn off a few began to question whether something had gone wrong.

The gunmen

Leader "Salim" - Awn Ali Mohammed: killed 2nd in command: "Faisal" - Shakir Abdullah Radhil: killed "Makki"- Makki Hanoun Ali: killed "Abbas"- Themir Mohammed Husein: killed "Hassan" - Shakir Sultan Said: killed Fowzi Badavi Nejad: sentenced to life imprisonment

Hostages reported that some of the gunmen who had been killed had thrown down their weapons and surrendered before the SAS shot them.

Some questioned why the Foreign Office did not allow Arab diplomats to help mediate negotiations as the gunmen had demanded.

The one surviving gunman, Fowzi Nejad, 22, was sentenced to life imprisonment nine months later.

The judge said he had taken part in an "outrageous criminal enterprise", causing "unspeakable terror, anguish and distress".