The announcement came after police said they raided two Internet cafes near the homes of some suspects and a news report said officers may have found a rifle and a pistol in a search of woodlands in the same area.
Travelers still faced problems at Britain's main airports, where flight delays and cancellations exacerbated confusion over shifting rules on hand luggage.
London's Metropolitan police said the latest suspect was detained around noon in the Thames Valley area just west of London. They offered no more details, including the person's gender or identity.
"A suspect has been arrested in connection with the investigation and is in custody in the Thames Valley area," a spokeswoman said, speaking on condition of anonymity to comply with department rules.
The developments came after several days of near silence from British officials, who had announced Thursday that they foiled the planned terror attack by arresting 24 people around the country. Police have released little information since then.
But CBS News correspondent Sheila MacVicar reports that one of the suspects, Tayib Rauf, was caught on closed circuit TV, unaware the police were also watching, just two hours before he was arrested last week. The video was shot around midnight, when Rauf was in a Birmingham grocery store chatting with the staff and collecting a payment for delivery of his family's baked goods.
The shop owner, Abid Hussein said: "He's not the sort of person, who, you know, is going to blow himself up at 2 o'clock in the morning."
But now the Rauf family that is now at the center of the investigation. Their home has been sealed off and police have taken away bags of documents and computer hard drives.
Under British law, authorities have until Wednesday to provide some details of their evidence. They are scheduled to do so when a judge holds a closed-door hearing to decide whether to extend detention for 23 suspects. One suspect was released without charge Friday.
The two Internet cafes were raided Thursday in central Slough, 25 miles west of London, not far from the High Wycombe neighborhood where several suspects were arrested, Thames Valley police said.
Police said they had increased their presence in Slough, and urged people to stay calm.
"There is no intelligence to suggest that there is any specific terrorist threat to anyone in this area," Chief Superintendent Brian Langston said.
Langston didn't say if police found anything in their search. Nargis Janjua, co-owner of the One World Internet Cafe, said officers arrived Thursday afternoon and removed 25 computers from her shop and loaded them into a van.
"They told us they were watching for days and weeks before," she said, adding that she had no idea why police were suspicious of activities in the shop.
The British Broadcasting Corp. said a search of woods in High Wycombe turned up several firearms and other items of interest. It was not clear if they were tied to the alleged plot, which authorities say involved plans to smuggle liquid explosives hidden in hand luggage aboard airplanes.
Investigations are also under way in Pakistan, where officials are holding 17 people, including British citizen Rashid Rauf, who they said has al Qaeda connections and was a key player in the plot. At least one of Rauf's brothers was arrested in England.
Pakistan's Foreign Ministry said the country might extradite Rauf to Britain, but had not yet been asked. "We do not have any extradition treaty at the moment but yes, because he is a British national, the possibility of his extradition remains there," ministry spokeswoman Tasnim Aslam said.