One of three men arrested on suspicion of being part of an Al Qaeda plot has been released without charge.
The man in his 30s was detained at a residential address in Luton, and released on Monday.
Police are still questioning two other men - one in his 20s arrested at Alliance Healthcare offices in Letchworth, Herts., and another in his 20s at another address in Luton.
The suspected target of the reported plot could have been a US Independence Day celebration at RAF Feltwell in Norfolk.
Officers from the Metropolitan Police’s Counter Terrorism Command arrested the men on July 14 as part of an ongoing investigation into Islamist-related terrorism.
They were arrested under the Terrorism Act on suspicion of being involved in the commission, preparation or instigation of acts of terrorism.
The warrant for arrest, granted to officers on July 15 for seven days, is due to expire tomorrow evening (Weds).