Trudie Styler, campaigning wife of pop star Sting, accompanied Janis Sharp and presented Mrs Brown with a petition compiled by the National Autistic Society, which requested a halt to McKinnon's extradition to face hacking charges in a US court (pictured).
"As each day passes with extradition still looming, it further breaks Gary's spirit not to mention the hearts of all his family, friends and supporters," said Sharp. "I just beg Mr Brown to act and put a stop to this living nightmare."
She called for McKinnon to be prosecuted in the UK on the grounds of medical evidence that since he had Asperger's Syndrome, a form of autism, extradition to the US could cause him severe mental health problems.
The High Court heard last month how it was possible to try McKinnon in the UK. It also heard that it would be humane to do so, to avoid submitting him to unnecessary suffering.
Trudie Styler and Sting have been lobbying the government on McKinnon's behalf. Styler said: "Gary's actions were clearly misguided. However extraditing him 7 years after the event and subjecting him to lengthy prison sentence thousands of miles away from his family is an unnecessarily cruel and undignified way to treat anyone, let alone someone with his condition."