Agree. But, FWIW, Alan Rusbridger, the author of the article, explains in the comments that in this case, this would not be legal, as the conversations he is quoting from took place after he had agreed to keep names off the record.
http://discussion.theguardian.com/comment-permalink/26170409
Perhaps another good journalist could score a one-up on this one? That aside, it doesn't seem coherent that the owner of the laptop containing the sensitive materials would voluntarily agree to conceal the names of the agents, and at the same time let their machine/drives be destroyed by the same sleuths (crooks?).
Seems fishy, but then what is not given the circumstances.
Since journalists have showed willingness to go to jail but to protect their sources they take things such as these very seriously.