The home secretary, Alan Johnson, pledged today to examine new medical evidence in the case of the computer hacker Gary McKinnon "very carefully" before approving his extradition to the US on charges of breaking into the Pentagon's military networks.

Johnson told MPs he had "stopped the clock" on proceedings to give McKinnon's lawyers time to consider medical reports and make legal representations.

The home secretary was today also pressed to delay further until an investigation into the US-UK extradition treaty had been carried out by the Commons home affairs select committee.

The 43-year-old, from Wood Green, north London, suffers from Asperger's syndrome, a form of autism, and says his hacking was aimed at nothing more than searching for reports of UFO sightings. His supporters fear his health would suffer in a maximum security jail in the US.

He had challenged Home Office decisions allowing his extradition to go ahead and the refusal of Keir Starmer QC, the director of public prosecutions, to put him on trial in the UK on charges of computer misuse. He failed in his high court bid to avoid extradition in July.

Johnson said the high court had already dismissed applications for McKinnon to be tried in the UK.

He said: "We have stopped the clock ticking on the representation to the European court because new medical evidence has been provided.

"There are two issues upon which Gary McKinnon's legal advisors have argued: the first is that the director of public prosecutions should have tried him in this country.

"The high court in July dismissed that, and wouldn't allow it to go to judicial review."

"I have to ensure that his Article 3 human rights are being respected. It's that new medical evidence that I will be looking at very carefully".

McKinnon's MP, David Burrowes, said the new medical evidence was "compelling" and detailed the effect extradition would have on McKinnon's Asperger's.

The Conservative MP for Enfield Southgate urged the home secretary not to execute the extradition order until after the select committee inquiry on 10 November.

When McKinnon was refused permission to appeal to the supreme court earlier this month, Lord Justice Stanley Burnton, who also heard his earlier high court appeal, said extradition was "a lawful and proportionate response" to his alleged offending.

He said McKinnon would be unlikely to succeed with his claim that extradition would breach his right to a private and family life, under Article 8 of the European Convention of Human Rights.

Nor did the court think that extradition to the US would be a breach of his right not to be subjected to inhuman or degrading treatment under Article 3.

In August, Labour's deputy leader Harriet Harman said that if McKinnon were convicted by an American court, Britain would move quickly to arrange for him to serve any jail term in the UK.