One of the world's foremost legal experts is to advise the official inquiry into the Iraq conflict, it was announced today.

Dame Rosalyn Higgins, a former president of the International Court of Justice, has been appointed to assist the panel on legal issues as well as the wider investigation.

Advice is also being sought from ex-Chief of General Staff General Sir Roger Wheeler, who was head of the British Army between 1997 and 2000.

The inquiry, which started work at the end of July and is being chaired by career civil servant Sir John Chilcot, is examining the period from 2001 to the end of July 2009.

It will consider the UK's involvement in Iraq, how decisions were made and will identify lessons that can be learned.

Dame Rosalyn served as president of the International Court of Justice (ICJ) in The Hague, Netherlands, from 2006 until she stepped down early this year.

The Cambridge graduate was the first woman to be elected judge of the ICJ, and her tenure included a historic ruling on whether Serbia was guilty of ethnic cleansing during the Bosnian war - the first time the ICJ had made such a ruling.

The court cleared Belgrade of direct responsibility for the Srebrenica massacre, but berated Serbia for failing to prevent it.

Yesterday the inquiry held the first in a series of meetings for bereaved families and Iraq veterans to say which areas they want it to examine.

Angry relatives of British servicemen killed in Iraq told Sir John and four inquiry members that Tony Blair must be held accountable for taking the nation to war.

In an atmosphere described as sombre and quietly emotional, many blamed the former prime minister for the deaths of their loved ones in an "illegal" conflict, and some even called for him to be prosecuted for war crimes.

Sir John has confirmed that Mr Blair will give evidence and insists he and his committee will not shy away from criticising individuals.

Among those attending yesterday's session in London was Deirdre Gover, 63, whose son, Flight Lieutenant Kristian Gover, 30, was killed in a helicopter accident in Basra, southern Iraq, in July 2004.

Speaking afterwards, she accused Mr Blair of lying to the Cabinet and to the country in the lead-up to the war.

"I hold Tony Blair personally responsible for the death of my son," she said.

"My son as an officer was prepared to die for his Queen and country in a just conflict. This was totally unjustified and wrong, and I think that's what the inquiry will prove."

A retired senior army officer whose son was killed in Iraq questioned the legality of the war and said the British public was "lied to" before it started.

Former Lieutenant Colonel Colin Mildinhall, a veteran of the 1991 Gulf War, said: "I believe we were misled.

"I would particularly like the Iraq inquiry to look at the whole representation of intelligence, how it was used or misused in the approach to this war.

"I believe this country has been badly let down and been lied to. I would like to see some accountability."

His son, Lieutenant Tom Mildinhall, 26, of the Queen's Dragoon Guards, was killed by an improvised explosive device while in a Snatch Land Rover patrol in the southern city of Basra in May 2006.

Sir John told the meeting that formal hearings taking evidence from witnesses would start at the end of the year but there would be a break during the upcoming general election.

A session today will feature veterans, with further sessions in Manchester on Friday, in Edinburgh on October 21, in Bristol on October 23 and in Belfast on October 28.