Guardian journalist Glenn Greewald (Vincent Yu/AP)

The Guardian has released more details about how the destruction of hardware containing data from National Security Agency (NSA) leaker Edward Snowden went down in its London offices:

On Saturday 20 July, in a deserted basement of the Guardian's King's Cross offices, a senior editor and a Guardian computer expert used angle grinders and other household tools to pulverise the hard drives and memory chips on which the encrypted files had been stored.

As they worked, they were watched intently by technicians from the Government Communications Headquarters (GCHQ) who took notes and photographs, but who left empty-handed.

Guardian editor Alan Rusbridger reported receiving a phone call from senior figures in the government telling him: "You've had your fun. Now we want the stuff back." He said the newspaper was threatened with legal action if it didn't turn over or destroy the data stored in Britain.

The Guardian chose the latter option after attempting to explain to authorities that it had other copies in other countries and that the destruction of the data would not impede its journalism.