On September 24, 2002, the UK Government published a report that would go on to be infamously dubbed the "dodgy dossier".

Titled Iraq's Weapons of Mass Destruction: The Assessment of the British Government, the report contained a foreword by then-Prime Minister Tony Blair in which he called Iraq a "current and serious threat" to the UK.

Blair claimed Iraqi dictator Saddam Hussein had some weapons of mass destruction (WMD) that could "be ready within 45 minutes of an order to use them".

Hussein, he said, had the capability to use weapons abroad that he had already shown himself willing to use at home, such as in the 1988 chemical attack on Iraqi Kurds in Halabja, which is estimated to have killed as many as 5000 people.

Blair's "45-minute claim" was trailed heavily in the tabloid press, including The Sun and The Daily Star, and was covered prominently elsewhere in the media.

Then-House of Commons leader Robin Cook, who would eventually resign in protest against the invasion, wrote that he asked Blair in March 2003 if he worried that Saddam Hussein might use chemical munitions on British troops.

According to Cook, the Prime Minister replied: "Yes but all the effort he has had to put into concealment makes it difficult for him to assemble them quickly for use."

Two months later, a source - later revealed to be Ministry of Defence scientist Dr David Kelly - told BBC journalist Andrew Gilligan that the 45-minute claim was one example of how the dossier had been "sexed up".

In August, the Hutton Inquiry, which was launched to investigate the circumstances surrounding the death of Dr Kelly the month before, heard the 45-minute claim had come from a second-hand source who was "quoting a well-placed senior officer".

The source had passed the information on to MI6 but the information had not been corroborated, said then-armed forces minister Adam Ingram.

The dossier also claimed Saddam Hussein would be able to assemble a nuclear weapon within one to two years if he could obtain fissile material and other components.

It argued he had tried to do just that by seeking to buy "significant quantities of uranium from Africa".

US president George W Bush went on to use this intelligence in his State of the Union address in January 2003.

Nuclear expert Professor Norman Dombey, of Sussex University, claimed in July 2003 that Iraq already had enough uranium for "any conceivable nuclear weapons programme".

He added: "Nuclear weapons are difficult and expensive to build not because uranium is scarce but because it is difficult and expensive to enrich.

"Neither British security services nor the CIA seriously thought Iraq had a functioning enrichment plant that would have justified all the noise about nuclear weapons we heard before the war."

Documents obtained by Italian intelligence seemed to bolster the case for war when they purported to prove Iraqi officials had tried to purchase 'yellowcake' uranium from Niger - but they were discredited as forgeries.

In September 2004, the Iraq Survey Group (ISG), a US-led multinational mission sent to Iraq after the invasion to search for WMD, found no evidence Saddam Hussein had made "concerted efforts" to restart Iraq's nuclear weapons programme, which was shut down in 1991.

The ISG also reported it had found no evidence of illegal stockpiles of any WMD, and that Iraq's chemical and biological weapons programmes had also been shut down in the 1990s.

The only such weapons they discovered were old, abandoned chemical munitions.

It also claimed Saddam Hussein had intended to restart his country's WMD programmes at some point in the future after economic sanctions on his country had been lifted.

The organisation also noted Hussein had deliberately tried to mislead Western intelligence into thinking he did have WMD capability as he believed this would prevent the West from attacking him.

At the point of Bush's address in January, critics claim the US government had already decided to attack Iraq regardless of the evidence of a continued WMD programme.

Indeed, based on a White House memo leaked last year, Blair was said to be in favour of military action against Iraq from as early as March 2002 - a year before the invasion was launched.

The underlying intelligence claims that led the US, the UK and their coalition allies to invade Iraq in March 2003 have been discredited over the years.

The questions that remain revolve around why so much faulty intelligence was believed, or at least promoted, by so many.