The British hacker, Gary McKinnon?s legal team have said they will take their fight against his extradition all the way to the European Court of Human Rights on Monday, as the high court in England begins deliberation on whether to send him to the US authorities. The judgement on this latest appeal will take around two weeks.

Five Law Lords heard McKinnons? barrister, David Pannick QC, claim that the US had abused the process, by attempting to strong arm his client into accepting extradition and pleading guilty.

Pannick told the hearing: “If the United States wish to use the processes of English courts to secure the extradition of an alleged offender then they must play by our rules.”

It has emerged that in exchange for compliance, US prosecutors offered to withdraw a threat to block any application for McKinnon to be repatriated to serve most of his time in a UK jail. This is central to his lawyers claim.

If accepted, the bargain would reduce his sentence from eight to ten years, to three to four years. Combined with the UK parole system, he may only have to spend two years in prison.

In her evidence, McKinnon’s solicitor Karen Todner said that in their correspondence the US had told her that failure to play ball would mean “all bets were off” and that repatriation to the UK “would not occur”. This threat, charged McKinnon’s team, “sought to impose pressure to accept extradition and plead guilty”, and represented an unlawful abuse of the court process that was “disproportionate [and] reprehensible”.

Prosecutors exaggerated their influence over the repatriation process, said Pannick, and in a bid to secure McKinnon’s co-operation, and that had “made it all the worse”. Edward Fitzgerald QC, who provided supporting intervention at the hearing on behalf of the civil liberties charity Liberty, said: “What the prosecution [was] saying is ‘I have immense powers and I will use them against you’.”

McKinnon admitted to taking advantage of poor security in US systems to install covert software that gave him control of settings and access to files. Bizarrely he claims he was looking for evidence of UFOs. The US government’s claim he has cost the country hundreds of thousands of dollars of damage.

Acting for the US government Clare Montgomery QC, disputed this, saying that even if McKinnon had refused to cooperate he would have still been considered for a return to the UK. “This was very close to the type of plea bargaining that might occur here… this was not a case of ‘we [US prosecutors] can give or withhold the right to transfer [to the UK]’” she told the Lords.

Montgomery scorned calls for Gary McKinnon to face trial in the UK, saying: “He must have appreciated as he hacked into American computers that he was committing an act that would have had repercussions in America.”

The general consensus among the McKinnon’s team was that the case is poised on a knife-edge., but they remained upbeat

?Defeat would be a major blow, but McKinnon’s team said outside the hearing that it would be by no means the last stand. The precedent set by the European Court of Human Rights in the Babar Ahmad case makes a challenge there likely?, said solicitor Karen Todner.