7/7 inquests: MI5 officer will be visible to families
A "very senior" MI5 officer is to appear anonymously at the 7/7 inquests but will be visible to the relatives of those who died in the suicide bombings.
The coroner granted a request from Home Secretary Theresa May for "Witness G" to give evidence with anonymity.
However, Lady Justice Hallett refused to rule that the witness should be screened from the families.
Witness G will give evidence on whether the attacks on London public transport in 2005 could have been prevented.
Lady Hallett told the hearings at the Royal Courts of Justice in London: "The bereaved families have been waiting over five years to see this witness or a witness from the security service give evidence.
"The issue of preventability is exceedingly important to them. It has been at the heart of most of their submissions to me ever since my appointment as coroner."
Lady Hallett said she was confident it would make a "considerable difference" to the bereaved families to be able to see the witness give evidence "rather than hear the evidence come from a disembodied voice".
The coroner earlier ruled she has the power to exclude the public from certain hearings in the interests of national security - but that did not include "interested persons" such as the bereaved relatives.
The home secretary decided not to appeal against a High Court ruling upholding that decision.
Ms May applied for the witness to give evidence behind screens, unseen by everyone but the coroner, security-cleared staff and lawyers.
Lady Hallett said the home secretary "believes, on advice, that the witness should be protected in this way" because revealing their identity "would materially increase the risk to their safety".
It was also said there would be "a significant threat to national security, given the nature of the operations in which Witness G has been involved".
The witness was described by the coroner as "a very senior member of staff at MI5".
Lady Hallett said the media and bereaved families had accepted there was "the possibility of a very real threat of material increase in the risk to the very life of the witness, and therefore they have accepted that an order for anonymity should be made".
Referring to the bereaved families, the coroner said she had not seen the "slightest hint" they would wish to see anyone's life put in danger.
She said: "Provided sufficient protective measures are put in place, there should be no increased risk to the witness, other than that which would attach in any event to the witness giving evidence, albeit anonymously."
Clifford Tibber of Anthony Gold Solicitors, who are representing seven of the bereaved families at the inquest, welcomed the coroner's decision.
"They want to put a face, not just a voice, to the person who will hopefully provide the answers to their questions."
In the attacks on 7 July 2005 four suicide bombers detonated homemade devices on Tube trains at Aldgate, Edgware Road and Russell Square, and on a double decker bus at Tavistock Square. They killed 52 victims and injured more than 700 people.
The inquests are expected to last until March.