Britain and the US did not believe Iraq’s weapons programmes posed a “substantial threat” before launching the 2003 invasion that overthrew Saddam Hussein, the inquiry into the war has heard.

Former UK diplomat Carne Ross claimed that the Government “intentionally and substantially” exaggerated its assessment of Iraq’s weapons of mass destruction (WMD) in public documents.

Mr Ross, who was First Secretary responsible for the Middle East at the UK’s mission to the United Nations from 1997 to 2002, alleged that nuanced intelligence was “massaged” into “more robust and terrifying” statements about Saddam’s supposed WMD.

He said in a statement to the inquiry: “It remains my view that the internal Government assessment of Iraq’s capabilities was intentionally and substantially exaggerated in public Government documents during 2002 and 2003.

“Throughout my posting in New York, it was the UK and US assessment that while there were many unanswered questions about Iraq’s WMD stocks and capabilities, we did not believe that these amounted to a substantial threat.

“At no point did we have any firm evidence, from intelligence sources or otherwise, of significant weapons holdings.

“Most of the unanswered questions derived from discrepancies in Iraq’s accounting for its past stocks and the destruction of these stocks.”