Police were granted warrants to detain eight terror suspects until August 30, and one for a further 24 hours, a police spokeswoman told AFP.
Two of the eleven suspects arrested two weeks ago have been released without charge.
"This evening we were granted warrants for further detention for nine people," a police spokeswoman said.
Under British anti-terror laws, police can detain terrorism suspects for up to 28 days without charging them with an offence, subject to regular court approval.
Previous legislation only allowed police to hold terror suspects for
14 days without charge.
A total of 25 people have been arrested since police carried out pre-dawn raids in London and around Britain on August 10 in connection with an alleged terror plot to blow up US-bound passenger jets flying from London's Heathrow airport.
Eleven have since been charged, and the total number of suspects released without charge is now five.
The 11 accused - including a young mother and a minor - appeared in a magistrates’ court in London 12 days after police raids in and around the British capital.
Eight facing the most serious charges of conspiracy to murder and preparing acts of terrorism were told to return to court on September 4 to appear before Judge Anne Rafferty at the Old Bailey criminal court in central London – the traditional venue for Britain's biggest criminal trials.
The three others are to return to the magistrates' court next Tuesday.
Of the three, two were charged with withholding information about an impending terrorist attack.
The third, a 17-year-old youth who cannot be named because he is a minor, was accused of possessing a book about bomb-making, suicide notes and wills, and a map of Afghanistan with information "likely to be useful" to someone planning an attack.
The eight facing the most serious charges were men mainly from east London: Hussain, 25; Umar Islam, 28; Arafat Waheed Khan, 25; Ahmed Abdullah Ali, 25; Ibrahim Savant, 25; Waheed Zaman, 22; Assaid Ali Sarwar, 26; and Adam Khatib, 19.
They were followed by Cossar Ali, 23, the only woman accused and the mother of an eight-month-old son, and Mehran Hussain, 23.
Seven other people, including two Britons, are being held in Pakistan, where the authorities have suggested a possible link with Osama bin Laden's Al-Qaeda network, which carried out the September 11 attacks in the United States.