GARY McKinnon's mother voiced delight today after learning she may have the chance to give evidence to prevent her son's extradition to the United States.

The Commons' home affairs select committee, chaired by Labour MP Keith Vaz, has confirmed it is holding a one-off session to examine the extradition treaty between the US and the UK.

The session was prompted by the controversy surrounding the McKinnon case. The 43-year-old from Palmers Green, who suffers from Asperger's syndrome, is facing extradition to the US on charges of breaking into the Pentagon's computer systems.

Though an official list of witnesses has not been made public, Mr McKinnon's mother, Janis Sharp, today claimed "reliable sources" have said it is likely she will be asked to stand.

The aim of the session is to grill Home Secretary Alan Johnson on why US lawyers need only demonstrate "reasonable suspicion" for an extradition warrant to be granted in Britain when there is no reciprocal agreement for the Crown Prosecution Service in America.

It will also question whether the home secretary should be given discretion to try cases in the UK.

Mrs Sharp, 60, from Enfield, said: "If I get the chance to stand, it will be brilliant.

"I know their questioning is tough, but that is fine by me, because I know Alan Johnson will get the same treatment.

"I am happy to stand because I have the knowledge and the passion to help. It is my son's life on the line.

"Today I feel more hopeful than I have felt for a long time."

Wilson Sharp, 61, Mr McKinnon's stepfather, added: "At this stage in the process, this is a big step. We have a lot more avenues open to us now than we had two weeks ago."

Mr Vaz said: "The case of Gary McKinnon highlights the difficulties in the current extradition relationship between the UK and the US. It is clear that the US got a better deal from the extradition treaty.

"The treaty needs to allow ministerial discretion in exceptional circumstances, such as the case of Gary McKinnon."

Mr McKinnon's extradition is currently on hold while new evidence is considered.

The computer hacker was refused permission on October 9 to appeal to the newly created Supreme Court, but a dossier of new evidence has been handed to the Home Office by Mr McKinnon's solicitors.

Officials have put the 14-day deadline for extradition on hold while they consider the new information, reportedly about his psychiatric health.

Mr McKinnon admits hacking into the secure US systems when he lived in Crouch End, but says he was only taking advantage of lax security to look for evidence of UFOs.