David Cameron, leader of the Conservative party, is set to force a parliamentary vote on Gary McKinnon’s extradition.

An opposition day debate in parliament tomorrow will focus on whether the NASA hacker should face prosecution in the US for hacking 97 high-level government PCs in 2001 and 2002. He has claimed he was looking for evidence of aliens.

The government under Gordon Brown has agreed with US demands to extradite McKinnon to face trial in the US. But Cameron maintained it is not fair to extradite McKinnon when he has Asperger’s syndrome, and that if convicted he could end up in a high security jail “thousands of miles away from his home, his family and his friends”.

Critics believe the government be defeated in a vote because the Liberal Democrats and Labour backbenchers are siding with the Conservatives, arguing that 43-year old McKinnon should not be extradited.

McKinnon’s legal team will argue today in London’s High Court that the Director of Public Prosecutions was wrong to decide not to charge him in the UK for the crime. The DPP failed to “consider and analyse” expert medical opinion that McKinnon could kill himself if extradited, they will argue. Additionally, other British hackers of US computers have been prosecuted here.

Johnson has argued he cannot change the situation because the DPP decides on charges. Nevertheless, the DPP could face its decision not to charge being overturned.