Eleven people, including a woman and a teenager, have been charged today over an alleged plot to blow up transatlantic aircraft as police revealed that they had found bomb-making equipment and martyrdom videos during their searches.

In a highly unusual move, the head of Scotland’s Yard’s Anti-Terrorist branch detailed some of the items seized during the huge investigation that saw 23 people arrested on August 10 in London, Birmingham and Buckinghamshire.

Deputy Assistant Commissioner Peter Clarke said that in dozens of raids his officers had found the martyrdom videos, improvised explosives devices, suicide notes and wills of alleged co-conspirators and an annotated map of Afghanistan.

Mr Clarke gave warning that the threat from terrorism "is real, it is here, it is deadly and it is enduring".

He added: "First, there is evidence from surveillance carried out before August 10. This includes important, indeed, highly significant video and audio recordings.

"I can also tell you that since August 10 we have found bomb making equipment. There are chemicals, including hydrogen peroxide, electrical components, documents and other items.

"We have also found a number of video recordings - these are sometimes referred to as martyrdom videos. This has all given us a clearer picture of the alleged plot."

Standing next to Mr Clarke in Westminster, Susan Hemming, head of the Crown Prosecution Service Counter Terrorism Division, set out the charges against the suspects.

Eight of the 11 have been charged with two offences of conspiracy to murder. Ms Hemming added that they had also been charged under a new offence of preparing acts of terrorism contrary to section five of the Terrorism Act 2006.

All the charges relate to an alleged plot to manufacture and smuggle the component parts of improvised explosive devices on to aircraft and assemble and detonate them on board.

Three other individuals have been charged with other offences under the Terrorism Act 2000.

One, a 17-year-old, has been charged with possession of articles useful to a person preparing an act of terrorism and two others, including a woman, have been charged with failing to disclose information of material assistance that could prevent an act of terrorism.

The teenager is said to have had a book about improvised explosives devices, suicide notes and wills of co-conspirators and an annotated map of Afghanistan.

Mr Clarke said that officers had carried out 69 searches of flats, houses, business properties and open spaces.

As well as bomb making equipment 400 computers had been seized along with 200 mobile telephones and 8000 other items, including memory sticks, CDs and DVDs.

He said: "First, there is evidence from surveillance carried out before August 10. This includes important, indeed, highly significant video and audio recordings.

"I can also tell you that since August 10 we have found bomb making equipment. There are chemicals, including hydrogen peroxide, electrical components, documents and other items.

"We have also found a number of video recordings - these are sometimes referred to as martyrdom videos. This has all given us a clearer picture of the alleged plot."

Finishing his statement he said: "I would like to reassure the public that we are doing everything we can to keep you safe, for you to live your lives without being in constant fear.

"However, we must be realistic. The threat from terrorism is real, it is here, it is deadly and it is enduring. As we all look for explanations, we cannot afford to be complacent and ignore the reality of what we face.

"These are difficult times for all communities, but I can assure you that the police service will not flinch from its duty to protect the public."

Twenty-three people were arrested on August 10 in East London, Birmingham and High Wycombe, Buckinghamshire in a huge anti-terror operation. Eleven others are still being questioned and one has been released.

Ms Hemming said the decision to charge the suspects was taken only this morning. "Together with another senior CPS lawyer, I have been working with the police full time at New Scotland Yard for the last eight days.

"We have been carefully examining and assessing the evidence against each individual with the assistance of anti terrorist officers in order to come to charging decisions at the earliest practicable opportunity.

"This morning I made a decision that there was sufficient evidence and authorised, with the approval of the Director of Public Prosecutions, the charge of 11 individuals."

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