London mayor Boris Johnson has called on US president Barack Obama to call off Washington's seven-year quest to extradite Nasa hacker Gary McKinnon.

In his column in The Daily Telegraph, Johnson called the move "neocon lunacy", and said that the 43-year old Londoner who hacked into Pentagon and Nasa systems is no threat to American security.

"The British government is obviously too feeble to help Mr McKinnon and, even though the courts last week granted him another review, it is plain that the matter will simply drag preposterously and expensively on," wrote Johnson.

"It is time for the commander-in-chief to tell the US military to stop being so utterly wet, dry their eyes, and invest in some passwords that are slightly more difficult to crack."

Johnson also argued that the "legal nightmare" could continue indefinitely at taxpayers' expense if Obama does not step in.

McKinnon, who could face 70 years in a maximum security jail if extradited and found guilty, has not denied hacking into the military systems, but has always maintained that he was motivated only by a desire to find evidence of extra-terrestrial life.

Proceedings against him were postponed last week while Keir Starmer, the director of public prosecutions, reviews the case.

McKinnon's lawyers are hoping that he can be tried under the UK's Computer Misuse Act, and wants his Asperger's diagnosis to be taken into consideration.