Britain on Thursday approved the extradition a computer expert accused by the United States of perpetrating the world's "biggest military hack of all time." Gary McKinnon was arrested in June last year following charges by U.S. prosecutors that he illegally accessed 97 U.S. government computers -- including Pentagon, army, navy and NASA systems -- causing $700,000 worth of damage. Interior Minister John Reid has signed an order for his extradition, his ministry said. McKinnon, who could face up to 70 years in jail and fines of up to $1.75 million, said he was planning to appeal against the decision, telling BBC News 24: "I am very worried and feeling very let down by my own Government." The ministry said McKinnon now has 14 days to appeal. McKinnon, whose hacking name was "Solo," has admitted gaining access to U.S. government computers but denies causing any damage. He had tried to fight extradition, saying he was "already hung and quartered over there" and would not receive a fair trial. Prosecutors said McKinnon hacked into sensitive networks over a one-year period from February 2002, crippling U.S. defense systems in the wake of the September 11 attacks. At the time of the indictment, Paul McNulty, U.S. Attorney for the Eastern District of Virginia, said: "Mr Mckinnon is charged with the biggest military computer hack of all time."