The former head of MI6 backed the intelligence about Iraq's weapons of mass destruction despite his knowledge that a key source was a proven liar, the Chilcot report reveals.

In a letter to prime minister Tony Blair in July 2003, Sir Richard Dearlove said he was confident about the intelligence even though the agency had said the source was someone "who had lied from the outset".

Further revelations are emerging as the 2.6m word document is analysed and The Times reported how Blair only found out several months later that the source had been discredited. The source emerged in September 2002 and claimed Saddam Hussein was making chemical and biological weapons in evidence presented to the prime minister in an MI6 report.

The source later said that chemical agents were being storied in Iraq in "glass spheres", which "remarkably similar to the fictional chemical weapon portrayed in the film The Rock".

This information was not shared with weapons experts though and by February 2003, it was concluded that source had been lying, although his intelligence was reissued by MI6 in a report distributed two weeks after the invasion.

The report says Dearlove "should have made sure that Mr Blair and [Jack] Straw [the foreign secretary] were informed" about the withdrawal of the source, who was used to bolster the case for war.

"Given the controversy about the failure to find WMD and questions about whether the intelligence had been presented accurately after the conflict, Sir Richard Dearlove should have ensured that ministers were aware of the position."

Meanwhile the Guardian uncovered how the Chilcot report revealed that the government ignored strict controls on the frequency and length of operational tours endangering the mental and physical health of the troops.

"The government's decision to contribute a military force to a US-led invasion of Iraq inevitably increased the risk that more service personnel would be put in breach of the harmony guidelines.

"The issue of the potential pressure on service personnel was not a consideration in the decision."

These details of the report will be scrutinised by lawyers looking for areas where legal action could be taken such as civil claims for compensation if there is evidence of negligence.