Alan Foley is the smoking gun.
From interview with former CIA analysts Ray McGovern and David MacMichael on 17 Sep 2003:

RAY MCGOVERN: Alan Foley? Alan announced just three days ago that he was leaving, and he was head of the analytic section that had purview over weapons of mass destruction. It was he who suggested that those sixteen offending words not be included in the president’s State of the Union address. He was finally arm twisted into condoning that, with the assurance that it would be blamed on the British.

AMY GOODMAN: Well explain that. He says, and he testifies before Congress…

RAY MCGOVERN: Yes, he testified before the Senate Intelligence Committee that in discussions with a Mr. Joseph of the NSC, he suggested that since the agency didn’t vouch for the business about Iraq seeking uranium from Niger, that it ought not to be used in the President’s Sate of the Union address, and indeed they had managed to get it out of previous presidential speeches. So why did they want to put it back in there? Well, finally he was persuaded that well, let’s blame it on the British. Let’s say, according to a British report. And Foley said, I suppose that would be alright to blame it on the British. Now, they didn’t even say ‘according to a British report’. What the President said was ‘the British have learned’. That’s a lot different. We are pretty careful with words in the intelligence community, but that is what the President said, ‘the British have learned that Iraq was seeking uranium from an African country....

AMY GOODMAN: So Alan Foley is leaving. How significant is that, David MacMichael?

DAVID MACMICHAEL: I think it’s significant. The man cannot continue to identified, whether he supports the policy or not, as an intelligence professional. He can’t continue to be identified with a process that had been and is being corrupted.

(emphasis added)