The firearms officer who shot Jean Charles de Menezes at Stockwell Underground station told an inquest today how he had to prepare to face suspects that would not hesitate to kill themselves and those around them.

The officer, known as Charlie 12, said that he wanted people to understand his thought process and how he believed there was a real danger that he would not be alive to go home at the end of the operation after listening to briefings on the fatal day.

He said: "I was left in no doubt as to the type of suspect we were about to intercept - that they were prepared to take their own and others' lives and the danger faced would be immeasurable.

"I am trying to convey the emotion. As police officers we are trained to stick to the facts and avoid how you feel as if we are not involved and I wanted to put in my statement the emotion I was feeling at certain times when relevant information was given in order to make it more human."

Summarising his thoughts at the time, Charlie 12 said: "We were possibly about to face subjects who were trained and had attempted to commit atrocities on other human beings with complete disregard for their own lives.

"They had prepared devices in order to achieve this. There was a real tangible danger that if we didn't act quickly or correctly then there would be an extreme loss of life.

"How would you feel? What would you do? These devices could be concealed around the body, hidden from view. How would you act faced with that type of threat?

"These thoughts were composed by myself when I had written the statements after the incidents. It was for people reading or subsequently hearing for the first time my thought process or perhaps for them to maybe see the type of threat that we would have to face.

"I remember thinking that we were going to have to go up against these people with a totally unknown threat, the highest possible threat, certainly the highest possible threat that I could imagine coming up against and, as I have said before, the whole journey, if I can call it that, was an extremely emotional one for me both at the time of the briefing and listening to the nature of the threat and the danger these people posed and possibly not going home again at the end of the day."

Earlier this morning, an anti-terrorist officer who was tasked to stop De Menezes while the innocent Brazilian was travelling on a bus told the inquest that he was close to pulling the vehicle over when he got the call to stand down.

Detective Sergeant Piers Dingemans, said: "As I recall we were right behind the bus because racing through my mind was whether or not to put my vest on before we got to the bus."

He said he would not have thought that until he was close to stopping and getting out of his car.

But orders came through that he was to stand down. He said: "We were told CO19, firearms, were going to take control of the operation and the subject was now theirs and not ours."

The officer described walking into Stockwell Tube station in the immediate aftermath of the shooting as the people that had been on the same carriage as De Menezes were coming out.

"There was obviously an amount of hysteria and shock from some of the people coming out."

Charlie 12 was testifying at the inquest into Mr de Menezes’s death which is being held at a special court sitting at the Oval cricket ground, south London.

The officer was screened from the public and the press but was visible to members of the de Menezes family.

He and another man, known as Charlie 2, fired nine shots from point blank range at Mr de Menezes onboard a Northern Line train at Stockwell Underground station on July 22 2005.

Seven bullets hit him in the head, one missed and one misfired. Mr de Menezes, 27, a Brazilian, died almost instantly and the official cause of death was recorded as “severe disruption to the brain”.

The shooting occurred 24 hours after four men had attempted to repeat the carnage of the 7/7 bomb attacks by detonating explosive devices on three Tube trains and a London bus.

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