Two grieving mothers whose sons were killed fighting for the British army in Iraq took their long-running battle to force a public inquiry into the legality of the war to the House of Lords this morning.

Lawyers for Beverley Clarke and Rose Gentle will argue before an enlarged panel of nine law lords that the Government is obligated to hold an independent review of the decision to go to war under Article 2 of the European Convention of Human Rights (ECHR), which protects the "right to life".

They will argue that the Government is bound by the convention to safeguard soldiers' lives by not sending them to fight in an illegal war. If the mothers win their appeal, it could result in Tony Blair, Lord Goldsmith, QC, the former Attorney-General, and Geoff Hoon, the former defence minister, called upon to give evidence in public.

The mothers, who were both at the House of Lords this morning, have already lost in the lower courts after judges ruled that the ECHR governed domestic rather than international human rights. Although the Court of Appeal expressed "every sympathy" for the mothers, it also said that the matter was for politicians and not the courts to decide.

In hearing their appeal, the House of Lords will only consider whether the Government is required under human rights laws to hold an independent inquiry — not whether the decision to join the American-led invasion was lawful. Nevertheless, the case is considered so important it will be heard by nine law lords instead of the usual five.

Rabinder Singh, QC, representing the two mothers, told the House of Lords that the Government owes soldiers a special duty because they are “under the unique compulsory control of the State and have to obey orders.”

“There is what some people call a military covenant between the State and those who are literally prepared to put their lives at risk for the sake of their country,” he said.

Trooper David Clarke, 19, from Littleworth, Staffordshire, was one of two soldiers who died in March 2003 in a “friendly fire” incident west of Basra. Fusilier Gordon Gentle, 19, from Glasgow, of the Royal Highland Fusiliers, died in June 2004 in an improvised explosive device attack on British vehicles, also in Basra.

Before the hearing Mrs Gentle told reporters outside the House of Lords: “It’s been five years now; what have they [the Government] got to hide?”

Phil Shiner, the lawyer for the claimants, said the case addressed the issue of ”whether there are some questions of law which are ruled out of bounds simply because there is a political background”. In the petition to the law lords asking them to consider the case, lawyers called the basis for going to war in Iraq the most important legal issue in a generation.

The hearing is expected to last three days.

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