The British Government stood by its official dossier last September, but the White House conceded for the first time that there were problems with prewar intelligence.

The International Atomic Energy Agency has said that documents that claim to show trade was taking place between Iraq and Niger were forgeries.

But Downing Street has always claimed that it had separate sources for the alleged resumption of uranium trade between the two countries, and did not rely on those documents.

The American admission was prompted by a declaration by a former US ambassador that he had told the Administration 11 months before Mr Bush’s speech in January that the uranium evidence was bogus.

Joseph Wilson was sent to Niger by the CIA last year to investigate British claims that Iraq had tried to purchase uranium. He concluded that there was no truth to the allegations.

Ari Fleischer, the White House spokesman, said yesterday that Mr Wilson’s report did not reach the White House.

There has been no satisfactory reason given as to why Mr Wilson’s conclusion, which he gave to the CIA and the State Department, had not been passed to Mr Bush’s speechwriters.

Mr Bush said in his State of the Union speech that “the British Government has learnt that Saddam Hussein recently sought significant quantities of uranium from Africa”.

But after first standing by that claim, the White House yesterday abandoned it, saying: “There is other reporting to suggest that Iraq tried to obtain uranium from Africa. However, the information is not detailed or specific enough for us to be certain that attempts were in fact made.”

One senior administration official said: “We couldn’t prove it, and it may in fact be wrong.”

The first mention that Iraq was searching for uranium in an African country appeared in the British Government’s dossier. Niger was not identified as the country.

The implication of the White House statement was that Mr Bush regarded that piece of British intelligence as unreliable.

However, British officials said yesterday that MI6 remained satisfied that the intelligence about Iraq’s “intentions” of buying uranium from Niger was correct. They pointed out that the original source of the intelligence had come from another country.

The information had been checked. The officials said that the United States was not told of the Niger connection because the information had been passed only to the British.

Under protocols recognised around the world, an intelligence agency can pass on information to an agency in another country only if approval is given. Permission was not given to the British Government in this case to pass the intelligence to the Americans.

However, the Americans were already aware of the connection, because the CIA had sent Mr Wilson to Niger to check whether the Iraqis had made contact to buy uranium.

One British official said that the diplomat “went to Niger to ask if the Iraqis had shown interest in buying uranium, and was told: ‘No.’ ” The official said: “That was it.”

The official said: “All the British intelligence dossier said was that the Iraqis had intent to buy uranium from an African country, it didn’t say that they had gone there and bought uranium.”

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