LONDON — British authorities charged 11 of the 23 suspects held in connection with an alleged plot to blow up trans-Atlantic airliners.

Eight were charged with conspiracy to murder and preparing acts of terrorism, Susan Hemming of the Crown Prosecution Service told reporters yesterday in London. Three others face related charges. Investigators found martyrdom videos, bomb-making equipment, electrical components, and chemicals including hydrogen peroxide, the head of the anti-terrorist branch of London’s Metropolitan Police, Peter Clarke, said during the news conference.

Each of the eight charged with conspiracy to murder intended “to smuggle the component parts of improvised explosive devices onto aircraft and assemble and detonate them on board,” the CPS said in an e-mailed statement. Eleven suspects remain in custody, and a female suspect was released, Ms. Hemming said.

The suspects were arrested when British police raided dozens of premises on August 10 after intelligence services said bombers were days away from using liquid explosives to attack American-bound flights from Britain. The investigation prompted chaos at airports, with more than 2,380 flights from London canceled in the week following the arrests.

The investigation was “immense” and “spans the globe,” Mr. Clarke said. “Highly significant” video and audio surveillance of the suspects had taken place before the August 10 arrests, he said.

Police have searched 69 sites and taken 400 computers, 200 cellular phones, and 8,000 computer items such as memory sticks, CDs, and DVDs.Some 6,000 gigabytes of data had been removed from the computers alone, and it will take months to examine the electronic records, Mr. Clarke said.

Ahmed Abdullah Ali, Tanvir Hussain, Umar Islam, Arafat Waheed Khan, Assad Ali Sarwar, Adam Khatib, Ibrahim Savant, and Waheed Zaman were charged with conspiracy to murder and preparing acts of terrorism, the CPS said without giving their ages or addresses.

A 17-year-old boy was charged with having a book on explosives along with suicide notes and wills in the names of people preparing to commit a terrorist act, the CPS said. He is also accused of having a map of Afghanistan that could have been useful to a terrorist, the CPS said. Under British law, the names of suspects under 18 are not released when they are charged.

Cossar Ali was charged with not disclosing information about another suspect, Ahmed Abullah Ali. An 11th suspect, Mehran Hussain, was charged with not disclosing information about another suspect, Nabeel Hussain, the CPS said.

Those charged will appear at the high-security Belmarsh Magistrates Court in southeast London tomorrow, a CPS spokeswoman, Anabelle McMillan, said in a telephone interview. The other 11 in custody were still under “active investigation,” Ms. Hemming said. “We cannot yet make a decision about whether further charges will follow,” she said.

Under recent British antiterrorism legislation, police can hold suspects for up to 28 days from the time of arrest, subject to regular court review. Police want the limit extended to 90 days. Civil liberties groups say 28 days is already the longest period allowed in any Western European country.

Police yesterday did not say where the bomb components mentioned were found. Officers using pitchforks have been combing undergrowth in King’s Wood in the town of High Wycombe, west of London. The August 10 raids took place in east London, High Wycombe, and England’s Midlands region.

All 43 police forces in England and Wales are now involved in the investigation — codenamed “Operation Overt.” They have all sent, or are sending, officers to help with the inquiry, which is led by the Metropolitan Police and involves MI5, Britain’s domestic spy agency.

Home Secretary John Reid said police are “convinced” that a plot was in the works to blow up airliners. The police investigation produced “substantial material that would allow them to take forward the judicial process,” Mr. Reid said Sunday in an interview with ABC News.

After talks with Mr. Reid last week, the European Commission vice president, Franco Frattini, said he would present European Union proposals on the detection and traceability of liquid explosives. He suggested measures including blocking Web sites that incite people to commit terrorist acts and using biometric indicators to profile passengers in advance. British Islamic groups last week urged police to back up the allegations against Muslims, saying the lack of information was causing cynicism.

The Muslim Council of Britain, an umbrella group founded in 1997 by more than 250 Islamic groups, criticized the police last week for not disclosing more information about the progress of the investigation. Muslims in Britain number 1.6 million, or about 2.8% of the population, according to the Office for National Statistics.

Pakistan has told America that a Qaeda leader linked to the alleged plot is based in the Kunar province of eastern Afghanistan, which borders Pakistan’s tribal areas, Agence France-Presse reported, citing Pakistani security officials last week.