You're right to advise caution, but I'm sure the memos are not fake. Apart from having a reputable source (a Cambridge academic, no less, see the summary and analysis link in the "one more memo" post in this thread) they were actually acknowledged as genuine by the Foreign Office at the time. Read on for details...
The forged memo (that I know of anyway) was one circulated to the UK press at the end of April, 2005, which purported to be legal advice from the UK Attorney General, advising Blair the Iraq war would be illegal. It was never published anywhere (AFAIK), and the police were alerted. Shortly afterwards, the actual advice
was published.
Despite the
conviction of many freepsheep, this was not the now famous DSM, which was from and to different people, on a different subject, and never denied by the British Government (Blair's comment was that it contained "nothing new"!).
Neither are the memos I've published the same "fake memo". They were substantially reported in the British press in late 2004, and were acknowledged as genuine by the UK Foreign Office.
See, for example, the Guardian story at:
http://www.guardian.co.uk/Iraq/Story/0,2763,1308368,00.html
The documents from the Cabinet Office and Foreign Office suggest that in March 2002 Mr Blair was concerned primarily about regime change rather than, as he subsequently said, weapons of mass destruction. Invasion simply for regime change would have been contrary to international law.
The Foreign Office yesterday acknowledged the documents were genuine but stressed they were only a snapshot of thinking at a particular time. Nor did they reflect the changes that took place over the following 12 months, in particular referring the issue to the UN, which the White House did at Mr Blair's behest, though it failed to get a second security council resolution authorising war.
--snip--
But Sir David Manning, then Downing Street foreign policy adviser, now UK ambassador to Washington, discloses in one of the newly emerged documents, a memo on March 14 2002, that at the time the main issue for Mr Blair was regime change.
He told Condoleezza Rice, Mr Bush's national security adviser: "I said you [Blair] would not budge in your support for regime change but you had to manage a press, a parliament and a public opinion that was very different from anything in the States."