In a scathing attack on Britain and the US, Mr Blix accused them of planning the war "well in advance" and of "fabricating" evidence against Iraq to justify their campaign.

Letting rip after months of frustration, he told the Spanish daily El Pais: "There is evidence that this war was planned well in advance. Sometimes this raises doubts about their attitude to the [weapons] inspections."

Mr Blix said Iraq was paying a "a very high price in terms of human lives and the destruction of a country" when the threat of banned weapons could have been contained by UN inspections.

The 74-year Swedish diplomat made clear that he believes he was misled by President Bush. At a White House meeting last October Mr Bush backed the work of Unmovic, the UN inspection team.

But at the time Mr Blix knew "there were people within the Bush administration who were sceptical and who were working on engineering regime change". By the start of March the hawks in Washington and London were growing impatient.