The Guardian is generally in sympathy with the liberal to left-wing ends of the political spectrum. This is reflected in the paper's readership: a MORI Poll taken between April-June 2000 showed that 80% of Guardian readers were Labour Party voters.
I think this may be wishful thinking on the part of the British Left.
Ya think? Ya mean it hasn't changed its stripes since its days as the ultra-left-wing Manchester Guardian? What does that have to do with its sources? The New York Times is far left but it breaks White House secrets almost weekly. Leakers are leakers the world over.