The Conservatives used the debate to highlight the case of Gary McKinnon
A Briton fighting extradition to the US for hacking into top-secret computers claims he was morally justified in breaking the law.
Gary McKinnon, 43, from Wood Green, north London, admits hacking into 97 US government computers, including Nasa's and Pentagon's, during 2001 and 2002.
He told the BBC he was on a "moral crusade" to prove US intelligence had found an alien craft run on clean fuel.
Results of judicial reviews into Mr McKinnon's case are due on Friday.
They focus on whether Mr McKinnon should have been allowed to face trial in the UK and whether the decision to extradite him should have been reconsidered in light of his diagnosis as having Asperger's Syndrome last year.
His lawyers say he is "eccentric" rather than malicious and that he should be tried on lesser charges in the UK to protect his mental health.
Mr McKinnon is accused of hacking into the computers with the intention of intimidating the US government.
His legal team fear he could be treated as a terrorist and face up to 70 years in jail.
The US government says his actions caused damage costing $800,000 (£500,000) at a time of heightened security in the wake of the 11 September 2001 attacks.
Mr McKinnon told BBC Radio 5 live's Victoria Derbyshire show: "I'm not blind to criminality but I was on a moral crusade at the time.
"There was good evidence to show that certain secretive parts of the American government intelligence agencies did have access to crashed extra terrestrial technology which could... save us as a form of free, clean, pollution-free energy.
"I thought if someone was holding on to that, that was actually unconstitutional under American law."
Mr McKinnon also criticised arrangements between the two countries that meant the US only had to prove "reasonable suspicion" to force extradition of a British citizen.
To extradite an American from the US, the British must prove "probable cause".
"It is actually a completely unbalanced extradition treaty. It should be a two-way street," said Mr McKinnon.
Earlier this month, the Conservatives failed in a bid to force a review of the law when their Commons motion was defeated by 54 votes.
Home Secretary Alan Johnson told them the 2003 treaty had simplified extradition procedures while safeguarding defendants' rights.
The burden of evidence required on each side is "essentially" the same, he added.