McKinnon's lawyer Karen Todner has told Associated Press that he will appeal the case to the European Court of Human Rights.
McKinnon has admitted hacking into computers belonging to NASA and the US military in 2001 and 2002 though he has disputed US prosecutors' claims that he caused $700,000 worth of damage.
McKinnon has previously told OUT-LAW that UK police told him on arrest that he would most likely receive a sentence of community service for the incident. US prosecutors have said that he could face jail terms of up to 70 years on anti-terrorism charges, McKinnon said.
US prosecutors are seeking his extradition. McKinnon has opposed the move and appealed it through the courts, eventually reaching the UK's highest court, the House of Lords.
McKinnon claimed that he was told that he would serve a three to four year sentence with less than a year in a low security US jail before being allowed to serve the remainder in the UK if he pleaded guilty and did not oppose extradition.
If he opposed extradition and did not plead guilty he would receive a sentence of eight to ten years at a high security US jail with no repatriation, he was told.
McKinnon's legal team argued that the size of the disparity between these two sentences put McKinnon under such pressure to plead guilty that it interfered with his human rights, and put him under inpermissable pressure to surrender his legal rights, particularly his right to contest extradition.
The Law Lords rejected that argument. "In one sense all discounts for pleas of guilty could be said to subject the defendant to pressure, and the greater the discount the greater the pressure," said Lord Brown of Eaton-under-Heywood in the ruling. "But the discount would have to be very substantially more generous than anything promised here (as to the way the case would be put and the likely outcome) before it constituted unlawful pressure such as to vitiate the process. So too would the predicted consequences of non-cooperation need to go significantly beyond what could properly be regarded as the defendant’s just desserts on conviction for that to constitute unlawful pressure."
Lord Brown said that the UK legal system does offer discounts on sentences for guilty pleas, and that negotiations are permitted. "It is accepted practice in this country for the parties to hold off-the-record discussions whereby the prosecutor will accept pleas of guilty to lesser charges (or on a lesser factual basis) in return for a defendant’s timely guilty plea," he said.
McKinnon's defence had cited a case involving Karl Goodyear from 2005 which it said forbade such plea bargaining. Lord Brown said, though, that this case only forbade such activity by a judge.
"What, it must be appreciated, Goodyear forbids are judicial, not prosecutorial, indications of sentence. Indeed, Goodyear goes further than would be permitted in the United States by allowing the judge in certain circumstances to indicate what sentence he would pass," he said.
Lord Brown said that the appeal should be rejected because none of the threats issued in the course of the US prosecutors' plea bargaining was serious enough to interfere with McKinnon's rights.
"In my judgment it would only be in a wholly extreme case…that the court should properly regard any encouragement to accused persons to surrender for trial and plead guilty, in particular if made by a prosecutor during a regulated process of plea bargaining, as so unconscionable as to constitute an abuse of process justifying the requested state’s refusal to extradite the accused," he said.
"It is difficult, indeed, to think of anything other than the threat of unlawful action which could fairly be said so to imperil the integrity of the extradition process as to require the accused, notwithstanding his having resisted the undue pressure, to be discharged irrespective of the strength of the case against him," he said.