By last week, however, the fallout from that intelligence had caused a senior White House aide, Lewis “Scooter” Libby, to be indicted on charges of perjury over the naming of a CIA officer.

Speculation mounted that two of the most powerful figures in Washington — Dick Cheney, the vice-president, and Karl Rove, political adviser to President George W Bush — would also be implicated in the scandal.

This is no Watergate or Lewinsky affair. It is a relatively arcane matter reflecting the mutual contempt of the vice-president and the CIA. But because it feeds on the increasingly bitter debate about the war in Iraq, it threatens the authority of an increasingly lame-duck second-term president.

The background to the scandal lies in Saddam Hussein’s attempts to rekindle his clandestine nuclear weapons programme in the 1990s, despite the United Nations sanctions regime, and in Cheney’s determination to see the dictator fall from power.

The information that reached London in 1999 came from MI6’s French counterpart, the DGSE. It arose from a visit made by Wissam al-Zahawie, an Iraqi diplomat, to Niger, the former French colony in west Africa. According to the DGSE, he was alleged to have asked President Ibrahim Bare Mainassara of Niger to supply Baghdad with the semi- processed uranium ore known as yellowcake.

The French had a finger in every pie in their former colony and their atomic energy commission controlled its uranium mines. They knew that Niger had provided Iraq with uranium in the 1980s.

It was only two months after UN weapons inspectors had left Iraq and both MI6 and the DGSE had been expecting Saddam to test the sanctions regime. So MI6 saw the intelligence as entirely credible. There were other reports that backed it up, including intercepted Iraqi communications, but only the French intelligence was conclusive.

Crucially, MI6 also believed that Saddam would be unable to restart his nuclear weapons programme until sanctions came to an end, a view which concurred with that of the International Atomic Energy Agency (IAEA), the UN’s nuclear watchdog.

The DGSE began an intelligence operation to block Saddam from obtaining uranium, urging its agents to find out all they could about his efforts. One of those who got involved was Rocco Martino, a former police officer who had worked for the Italian intelligence service between 1976 and 1985, when he was sacked for being a “chancer”. He tapped up contacts at the Niger embassy in Rome.

The French did not at the time pass their information to the CIA. Under the rules that govern intelligence exchange, MI6 could not do so without French permission, although it did pass on its own less conclusive evidence.

The Iraq-Niger nexus vanished from intelligence screens for two years. By the time it reappeared, global politics had been transformed by the September 11 attacks on America.

In October 2001, as Bush launched his war on terror, the CIA raised the yellowcake affair in its intelligence assessments for the first time. Its information came, however, from Italian sources, not French.

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