An inquest has heard police were prepared to kill Jean Charles de Menezes without orders.
Officers were ready to take a "critical" shot at the Brazilian if Deputy Assistant Commissioner Cressida Dick was unable to make the "career-threatening decision", a tactical adviser, known as Trojan 84, said.
The inspector, whose identity is protected during the inquest into Mr de Menezes death, told how he briefed the marksmen who shot dead the 27-year-old, who was mistaken for failed bombing suspect Hussain Osman.
Giving evidence for the first time in open court, he said: "We felt that for any DSO (designated senior officer - Ms Dick) to make a decision about a critical shot was a hugely difficult decision to make and maybe career-threatening.
"In relation to the critical shot, the instruction would come direct from the DSO but what I also mentioned was that if we were able to challenge, but the subject was not-compliant, then a shot may be taken."
When asked if officers were prepared to take the critical shot without word from his bosses, he replied: "Yes."
He added: "It was my job to tell the team they would be supported whatever decision they took because of the structures that were in place."
The inquest heard how firearms police were not deployed on transport networks in the wake of the July 7 bombings because officers were otherwise engaged.
Chief Inspector Vince Esposito, the senior adviser in the operations room at New Scotland Yard, said officers patrolling London's Underground were unarmed despite raised security fears.