I can't explain the copying and recopying, but given the evidence available on these memos, the idea that they're fake isn't going to fly.

PowerLine, no bastion of liberalism, comments here:

...I very much doubt that the documents are fakes, for two reasons. First, to my knowledge no one in the British government has denied their authenticity. The "Downing Street memos" are much different from the CBS National Guard documents in this important respect: the CBS documents were ostensibly authored by Jerry Killian, who had been dead for twenty years. The Downing Street documents, on the other hand, were allegedly authored by, and relate to meetings recently conducted by, a group of men who are very much alive and well. I can't conceive of a reason why they would fail to attack the documents' genuineness if there were a basis for doing so.

Second, if the Downing Street memos were fakes, they would say more. As we have noted before, the memo that has been most widely trumpeted on the left says little or nothing of significance. What it does do, however, is confirm the sincere worry at the highest level of the British government about the possibility that Saddam would use his weapons of mass destruction either against coalition troops, or against Kuwait or Israel. Here again, the contrast with the 60 Minutes documents is instructive. Those documents were neatly constructed to give the Democrats just what they needed to attack President Bush's Guard service. They provided the evidence that some on the left thought ought to exist, but in fact didn't. By contrast, the Downing Street memos, while interesting, are innocuous. If someone went to the trouble of faking them, I would expect him to fake something better.