The man was picked up last week near the border of Pakistan and Afghanistan.
The 24 suspects in custody are British born and bred, but intelligence officials believe someone from the outside was calling the shots in a complex plot to blow up planes over America.
Pakistani authorities think they found a link to Al-Qaeda. The arrest of a British national with suspected ties to the terror group's base in Afghanistan.
Most of the other two dozen detainees in the U.K. are of Pakistani descent. Among them, a heavily-pregnant woman, the mother of a small child and a worker at London's Heathrow airport. But British authorities fear more suspects are still out there.
Tight security at the terminals is locked in place. Passengers were forced to reveal the few things they're allowed to carry on flights to the U.S.
Amy Nielsen, a Colorado traveler, said, "As long as we're safe, I guess I'll deal with the four hours delay as long as we can be safe flying."
Detectives say suspects had plans to use cameras and iPods to detonate liquid explosives in as many as 10 planes while over American soil, and they're interrogating some two dozen suspects.
While not everybody in Britain is convinced these are the faces of terrorists, it will be for British investigators to decide as they piece together all the details of the broken plot.