The move follows several weeks of behind-the-scenes work by McKinnon's legal team, Infosecurity understands. McKinnon's lawyer, Karen Todner, said she was "delighted" by the decision, which means that the UK hearing will probably take place in April or May.
At the hearing, the plan is for the judge to rule on whether the Home Secretary was right to decide that sending him to the US for trial would not breach his human rights. Todner, however, has warned that McKinnon – who suffers from a form of autism known as Aspergers Syndrome – is in a "very poor mental state" because of stress.
She added in a press statement that: "I am delighted that the High Court has agreed to grant permission for the judicial review of Alan Johnson's decision to extradite Gary McKinnon. However, that is countered by the very poor mental state of Mr McKinnon due to the ongoing pressure of these proceedings. I would urge Mr Johnson to review his decision and I appeal to President Obama to withdraw the application for extradition. Mr McKinnon's suffering has gone on long enough."
As reported previously, last November the Home Secretary rejected the application to stay the extradition, saying he had "no general discretion" to refuse the request from the US government. In its own press statement, the Home Office said yesterday that it had "noted" the court's decision.
McKinnon's mother, Janis Sharp, told reporters that she felt "incredible, indescribable" relief over this latest legal decision.
"I can't believe it – some common sense at last. This judge has made such an honourable and decent decision. We've fought for so long for compassion and understanding. Gary's health has badly declined, it's been traumatic to see," she said.
Reaction to the news has been highly positive, with Liberal Democrat Leader Nick Clegg – who has campaigned hard on McKinnon's case – telling the BBC that the judicial review was heartening news. "Even now the Prime Minister and Home Secretary could step in to spare Gary McKinnon from this ordeal by ensuring that he is instead tried in a British court," he said.
"It must be hoped that the courts prevent this unfair extradition and in doing so display more courage than our ministers," he added.
North of the border, Alistair Carmichael, the Liberal Democrat shadow Scotland secretary said that the whole legal circus could end tomorrow.
"For as long as legal proceedings are still live in this country, there's still hope for justice for Gary McKinnon," he commented. "This whole legal circus could be ended tomorrow if the government had the guts and the compassion to stand up to the US administration and tell them that they will not send Gary to the States," he added.