The suspect, who was not named, is the seventh man bailed in the investigation of an apparent plot aimed at RAF Fairford air base, which has been used by US bombers to strike Iran.
United Kingdom authorities have linked the incident to Iran.
Police are continuing to investigate the incident that led to scores of residents being urged to leave their homes near the base on September 27 as armed police officers and army bomb-disposal experts swarmed the rural area.
Police later said they had found a quantity of an accelerant - petrol - in three vans linked to the initial five suspects but no explosives.
Metropolitan Police commissioner Mark Rowley urged the public to "trust" the police probe on live radio after being asked by a listener during an LBC phone-in why suspects in the case had been released.
"We can't talk about all of our intelligence that we've got behind it" but insisted the investigation was "progressing extremely well," Rowley said.
"You will see more progress on this investigation.
"I know this is a really difficult thing in a world where everything is so open and transparent but please give the police time and trust us," he added.
Pressed by presenter Nick Ferrari on whether he knew if the incident was a "dummy run" attempt at a terror plot, if the suspects were seeking diplomatic immunity as has reportedly been suggested and why they called the police, the Scotland Yard boss said: "I know all of the above and lots more. Please trust us and you will see the investigation continue to develop".
with PA
