There is no freakin' way a reporter would destroy the originals. Maybe put them in a safe deposit box, mail them to himself, give them to a trusted friend to hide, etc., but not destroy them!
Those originals would potentially net him a Pulitzer, and possibly a legacy, if this story actually brought down world leaders. No way would he burn that glory source.
The originals will net him and his source a nice long term in a British jail for violating the British Secrets Acts.
could Burkett have supplied these documents as well? Maybe he had a bone to pick with PM Blair & CO?